I Ching Hexagram 18: Work on the Decayed - Meaning, Changing Lines and Guidance

I Ching Hexagram 18, Work on the Decayed, is Mountain over Wind and means an inherited situation has spoiled through neglect and is now yours to repair. This guide covers the Judgement, the Image, all six changing lines, the nuclear Hexagram 54 and opposite Hexagram 17, and how Hexagram 18 reads for a decision, a relationship and work.

What does Hexagram 18 Work on the Decayed mean in the I Ching?

Hexagram 18, Work on the Decayed, means that something you are responsible for has been quietly rotting while nobody attended to it, and that the answer is repair rather than escape. The Chinese name is Gu, written with three insect characters stacked over a vessel: a bowl of food set down, covered, and left standing until what is inside it breeds. The whole Hexagram 18 meaning follows from that bowl. Nothing dramatic happened. A dish was put down, and time did the rest. Hexagram 18 is unusual because it opens with the strongest possible endorsement and then hands you a job. The Judgement promises yuan heng, supreme success, and adds that it furthers one to cross the great water, the standard phrase for committing to a difficult undertaking instead of waiting. The good fortune in Hexagram 18 is not the situation. The situation is spoiled. The good fortune is the work. The Miscellaneous Notes appendix glosses Gu with a single word meaning to put in order. The Sequence of the Hexagrams glosses it as affairs, tasks, business to be handled. When Hexagram 18 appears, the oracle is not describing your mood. It is naming a chore that has your name on it.

What makes Hexagram 18 distinctive is that the decay it names is almost always inherited. Five of its six line texts speak of setting right what was spoiled by the father or the mother. The reading assumes you did not create the mess; you arrived after it, and the only live question is whether you pick it up. That is why Hexagram 18 turns up so reliably for a family business, a house left by a parent, or a friendship drifting since a conversation nobody had. The hexagram carries a darker layer from Chinese folklore, where gu named a poison bred by sealing venomous creatures in a jar until one survived. The survivor was the poison. That gives Hexagram 18 its edge: the corruption is not inert. It grew, it fed on its own container, and given another season it will grow further. Readers who draw Hexagram 18 asking whether to wait get the same answer every time, since waiting is the mechanism that produced the reading.

Is Hexagram 18 a good or a bad omen in the I Ching?

Hexagram 18, Work on the Decayed, is a favorable omen attached to an unfavorable situation. Its Judgement opens with yuan heng, supreme success, which only a handful of hexagrams receive, but that success is conditional on carrying out the repair. Read as a forecast of conditions it is poor. Read as an instruction it is among the most encouraging answers in the Book of Changes.

What does the name Gu mean in Hexagram 18?

Gu, the Chinese name of Hexagram 18, is written as three insect characters above a bowl, and it carries three linked senses: a vessel whose contents have bred worms, an inherited or festering disorder, and affairs that need handling. The Miscellaneous Notes appendix reduces all of that to one gloss, to put in order, and that is the sense most translators follow.

How do Wilhelm and Legge translate Hexagram 18?

Richard Wilhelm rendered Hexagram 18 as Work on What Has Been Spoiled, with Decay in parentheses, in the German translation Cary Baynes later carried into English. James Legge, in his Sacred Books of the East version, kept the transliteration Ku and glossed the hexagram as the troubles or work to be dealt with. Modern versions title it Decay, Repair, or Remedying.

Which two trigrams form Hexagram 18, and why does Mountain over Wind produce decay?

Hexagram 18, Work on the Decayed, is Gen, the Mountain, above Xun, the Wind or Wood, below. Reading the six lines from the bottom upward, Hexagram 18 runs yin, yang, yang, yin, yin, yang. The lower three form Xun, wind and penetrating growth. The upper three form Gen, the mountain, whose defining quality in the trigram system is stopping. The combination produces decay by plain mechanics. Wind is the element that circulates and disperses. Put a mountain on top of it and the wind cannot rise. It runs along the base of the slope, turns back on itself, and stirs the same air over the same ground. Air that never leaves goes stale, and everything sheltered under that mountain sits in it. The pairing is also a family relationship in the trigram scheme. Xun is the eldest daughter and Gen the youngest son, so Hexagram 18 places the youngest above the eldest, an inversion of household order that classical commentators read as the structural reason things have gone wrong. Nothing is being attacked from outside. The arrangement inside the house is upside down, it has been that way for a long time, and by now it has begun to smell.

The two trigrams also explain why the remedy in Hexagram 18 works the way it does. Xun does not push. Its image is wind that gets into a room through the gaps, and its action is penetration by persistence rather than force. Gen does not act at all; it holds a boundary. So the corrective energy of Hexagram 18 is patient infiltration underneath a fixed limit, which is what repairing an entrenched situation actually feels like. You cannot move the mountain, so you work under it, one gap at a time. Xun's second image is wood, and wood is what boats are made of, which is how classical commentary justifies the Judgement's promise about crossing the great water. The means of crossing is already present in the lower half of Hexagram 18. Turn the picture around and it becomes a warning: wind under a mountain also erodes it, invisibly, over years. The decay in Hexagram 18 cuts both ways, spoiling the contents while hollowing out the structure that looked permanent.

What is the line structure of Hexagram 18 in the I Ching?

Hexagram 18, Work on the Decayed, reads from the bottom line upward as yin, yang, yang, yin, yin, yang: a broken line at the base, two solid lines, two broken lines, and a solid line at the top. Lines one through three form Xun, wind; lines four through six form Gen, mountain. In King Wen order it is the eighteenth hexagram, following directly after Hexagram 17, Following.

What does the Mountain trigram Gen contribute to Hexagram 18?

Gen, the Mountain, sits in the upper half of Hexagram 18 and contributes stopping, boundary, and stillness. In the repair reading it is the inherited structure that will not move: the family arrangement, the institution, the old decision nobody revisits. Gen is why Hexagram 18 counsels working underneath and inside a situation rather than confronting it head on, and why its top line finally steps outside the arrangement altogether.

What does the Wind trigram Xun contribute to Hexagram 18?

Xun, Wind and Wood, sits in the lower half of Hexagram 18 and contributes penetration, gentleness, and gradual entry. Trapped under the mountain, Xun is the stagnant air that lets the contents spoil. Released as a method, it is the patient, low-force approach that clears an entrenched mess. Xun as wood also supplies the boat implied by the crossing of the great water.

What does the Hexagram 18 Judgement say about crossing the great water and the three days before jia?

The Judgement of Hexagram 18, Work on the Decayed, reads: work on what has been spoiled has supreme success; it furthers one to cross the great water; before the starting point, three days, after the starting point, three days. Each clause does specific work. Supreme success, yuan heng, is the highest grade of endorsement in the Book of Changes, and Hexagram 18 attaches it to a rotten situation, which is the entire point. A spoiled thing fully attended to yields more than an untouched thing left alone. Crossing the great water then rules out the passive option. Hexagram 18 does not permit managing the decay from the shore; the repair requires committing resources you cannot take back. The third clause is the one readers stumble over. The Chinese counts three days before and three days after jia, the first of the ten heavenly stems that ordered the old calendar. Jia marks a beginning, so the phrase brackets the start of the work with a fixed period of preparation on one side and a fixed period of follow-through on the other. Hexagram 18 does not ask for a decisive moment. It asks for a before, a start, and an after, and treats all three as one job.

Commentators have long noticed that the two stems the count lands on carry puns. Three days before jia is xin, which sounds like the word for new; three days after jia is ding, which sounds like the word for settling or attending carefully. Read that way, the Judgement of Hexagram 18 spells out its own sequence: understand what made the old thing rot before you begin, then supervise the replacement until it holds. Skip the first period and you rebuild the same fault. Skip the second and the repair itself decays. This is why Hexagram 18 is a poor answer for anyone hoping for a quick fix and an excellent one for anyone willing to schedule the whole arc. It contains no line that rewards speed, one line that punishes delay and one that punishes over-persistence, and between them sits this calendar image: begin at a marked point, with preparation behind you and attention ahead. Read for timing, Hexagram 18 usually indicates work already overdue, which is why it appeared at all, but not work to launch within the hour.

What does it furthers one to cross the great water mean in Hexagram 18?

In Hexagram 18, Work on the Decayed, the phrase it furthers one to cross the great water means the repair requires real commitment rather than management from a safe distance. The image is loading a boat and leaving the bank. Applied to a decayed inheritance, it rules out the half measures: patching, delegating quietly, or waiting for the situation to resolve itself.

Why does Hexagram 18 promise supreme success for a spoiled situation?

Hexagram 18 promises supreme success because in the logic of the Book of Changes a decayed situation holds unusual amounts of available gain. Nothing has been extracted from it for a long time, so the return on a genuine repair exceeds the return on maintaining something already healthy. The promise attaches to the work performed, not to the state of affairs the hexagram is describing.

What are the three days before and after jia in Hexagram 18?

Jia is the first of the ten heavenly stems in the traditional Chinese cycle, and Hexagram 18 brackets it with three days on either side. Counting back three stems lands on xin, counting forward lands on ding. Traditional readings hear these as new and as attending carefully, which gives the hexagram its two-part instruction: diagnose thoroughly before beginning, then supervise closely once the work has started.

What is the Image of Hexagram 18 and what does it tell you to do?

The Image of Hexagram 18, Work on the Decayed, reads: the wind blows low on the mountain, the image of Decay; thus the superior person rouses the people and strengthens their character. The first half restates the trigram picture. Wind pinned at the foot of a mountain circles instead of moving through, and everything under it stops being aired. The second half is the surprise. Given a picture of stagnation, the Image does not prescribe cleaning, purging, or punishing anybody. It prescribes two actions: stirring people up, and building up their virtue. That instruction is the practical center of Hexagram 18. The hexagram treats decay as a failure of energy and of formation rather than a failure of rules. Something stopped being tended because the people around it lost momentum and were never taught to keep it. Add rules on top of that and the rules rot too. Wake people up and train them, and the maintenance handles itself. Notice also that the Image is addressed to whoever holds responsibility, not to a lone repairer. Hexagram 18 is rarely a solo assignment. The mess is a household mess, a team mess, an institutional mess, and the fix runs through the people living inside it.

The two verbs in the Image of Hexagram 18 map onto its two trigrams. Rousing the people is Xun, the wind, getting movement back into air that has been standing still. Nurturing character is Gen, the mountain, building something with mass that stays where it is put. One is motion and the other is structure, and the hexagram insists on both. Motion alone produces a burst of cleanup that lapses within weeks; structure alone produces rules nobody has the appetite to follow. For a reader applying Hexagram 18 to a real situation, the Image is the difference between a weekend of frantic sorting and an actual repair. The frantic weekend is wind without mountain. The repair asks what habit or standard would have prevented the decay, and installs that alongside the cleanup. Notice also what the Image does not say. No blame is assigned anywhere. The father and mother of the line texts are never condemned, only their spoiled work is addressed, and that restraint sets the tone: fix the thing, spare the person.

Why does the Image of Hexagram 18 talk about rousing the people?

The Image of Hexagram 18, Work on the Decayed, prescribes rousing the people because the hexagram diagnoses decay as lost momentum rather than broken rules. Wind trapped under the mountain has stopped circulating, and the human equivalent is a group that quietly gave up on maintaining something. Restarting that movement is the first half of the repair.

Does Hexagram 18 assign blame for the decay?

Hexagram 18 assigns no blame. Its line texts name the father and the mother as the source of what was spoiled, then instruct the reader to set it right rather than to condemn anybody, and line one states outright that once the son takes the work on, no blame rests on the departed father. Repair without indictment is the tone of the whole hexagram.

What does Hexagram 18 mean by strengthening character?

Strengthening character in the Image of Hexagram 18 means installing the standard or habit whose absence allowed the decay, so that the cleanup holds after the effort fades. It corresponds to the mountain trigram in the upper half of the hexagram: something with enough mass to stay put on its own. Without that second step, Hexagram 18 predicts the same spoilage returning in the same place.

What do Hexagram 18 changing lines 1, 2 and 3 mean?

The first three changing lines of Hexagram 18, Work on the Decayed, cover taking the inherited job on, handling the delicate half of it, and pushing too hard. Six at the beginning: setting right what the father spoiled; if there is a son, no blame rests on the departed father; danger, and in the end good fortune. This is the moment of accepting the work. The line acknowledges risk, because taking responsibility for someone else's mess exposes you, and it ends well because the alternative is that the mess simply stands. Changing this line yields Hexagram 26, The Taming Power of the Great, which concerns force held in reserve. Nine in the second place: setting right what the mother spoiled; one must not be too persevering. A strong line in a yielding place, so Hexagram 18 restrains its own energy here. Some decayed things are delicate, bound up with feeling and long attachment, and forcing them breaks exactly what you were trying to save. Changing gives Hexagram 52, Keeping Still. Nine in the third place: setting right what the father spoiled; there will be a little remorse, no great blame. Excess again, and this time it shows, though the work still gets done. Changing gives Hexagram 4, Youthful Folly.

Read together, lines one through three of Hexagram 18 form the lower trigram Xun, and they behave like it: entry, first contact, working in from underneath. Line one is the decision to enter at all, and its danger is real. Whoever takes on a family firm, an abandoned project, or an estate is the person held to account for it from that day forward, which is why the line pairs danger with eventual good fortune instead of promising an easy run. Lines two and three form the clearest internal contrast in the hexagram. Both are solid lines, both concern setting right what a parent spoiled, and they differ only in what that strength meets. Line two meets something that must be handled softly. Line three meets something that absorbs pressure and merely notes the cost of using too much. Applying line three's approach to a line two situation is the most common way Hexagram 18 goes wrong: a correct repair carried out with force the relationship could not survive.

What does line 1 of Hexagram 18 mean?

Line one of Hexagram 18, Work on the Decayed, is a yielding line reading: setting right what the father spoiled; if there is a son, no blame rests on the departed father; danger, in the end good fortune. It marks the moment of accepting an inherited mess. The danger is the exposure of taking responsibility, and the good fortune follows from taking it anyway.

Why does line 2 of Hexagram 18 mention the mother?

Line two of Hexagram 18 names the mother because it is the one place where the hexagram's inherited disorder is treated as delicate rather than structural. The line is a solid line in a yielding position, and its instruction, that one must not be too persevering, warns that force applied here damages what the repair was meant to preserve. It changes to Hexagram 52, Keeping Still.

Is line 3 of Hexagram 18 a warning?

Line three of Hexagram 18 is a mild warning rather than a prohibition. Its text allows a little remorse but no great blame, meaning the repair goes through and the only cost is the roughness of the method. A solid line at the top of the lower trigram, it is the point where eagerness overshoots. It changes to Hexagram 4, Youthful Folly.

What do Hexagram 18 changing lines 4, 5 and 6 mean?

The upper three changing lines of Hexagram 18, Work on the Decayed, cover the refusal to act, the successful repair, and the exit. Six in the fourth place: tolerating what the father spoiled; in continuing one sees humiliation. This is the only line of Hexagram 18 with no way out of it. A yielding line in a yielding place has neither the will nor the strength to start, so it accommodates the decay and calls that accommodation peace, and the text is blunt about where that ends. Changing this line gives Hexagram 50, The Cauldron, a whole and honored vessel, which answers the spoiled bowl in the hexagram's own name. Six in the fifth place: setting right what the father spoiled; one meets with praise. This is the ruling line of Hexagram 18 and its best outcome. It sits in the position of authority while remaining yielding, which means the repair succeeds because the person doing it works through others rather than by personal force. Changing gives Hexagram 57, The Gentle. Nine at the top: he does not serve kings and princes, he sets himself higher goals. This is the one line that steps outside the work entirely. Changing gives Hexagram 46, Pushing Upward.

Line four is the line most readers recognize and least want to draw. The Chinese verb is tolerance, and Hexagram 18 treats tolerance of a spoiled inheritance as the failure mode of the entire hexagram. Not malice, not incompetence, just a decision to live alongside the rot because raising it would be awkward. The humiliation predicted is not a punishment. It is what happens when the decay finally becomes visible to everyone and the record shows you knew. Line five earns praise precisely because it does not fight. A yielding line in the fifth place completes the repair by drawing on capable help, the mature form of the wind trigram's method. Where line three pushes and pays for it, line five delegates and is thanked. The top line is the genuine oddity of Hexagram 18: after five lines of repair it produces someone who declines the arrangement to pursue something of their own, either an earned departure or a withdrawal that others must now cover.

Why is line 4 of Hexagram 18 the worst line?

Line four of Hexagram 18, Work on the Decayed, is its worst line because it is the only one that declines the hexagram's central task. Its text tolerates what the father spoiled and predicts humiliation for anyone who continues that way. A yielding line in a yielding place, it lacks both the position and the strength to begin the repair, so it settles instead for quiet coexistence with the decay.

What makes line 5 the ruling line of Hexagram 18?

Line five of Hexagram 18 governs the hexagram because it occupies the seat of authority and completes the repair the other lines only attempt, meeting with praise. Its yielding nature matters: the correction succeeds through cooperation and capable helpers rather than personal force. It is the outcome the Image points at in rousing the people and strengthening their character.

What does the top line of Hexagram 18 mean about not serving kings and princes?

The top line of Hexagram 18 describes someone who does not serve kings and princes but sets himself higher goals, a person stepping outside the inherited work altogether. Placed above the mountain trigram, beyond the reach of office, it can mean an earned retirement from the family repair or an abdication that leaves the job to somebody else.

What are the nuclear and opposite hexagrams of Hexagram 18?

The nuclear hexagram of Hexagram 18, Work on the Decayed, is Hexagram 54, The Marrying Maiden, and its opposite is Hexagram 17, Following. The nuclear hexagram is built from the inner lines. Taking lines two, three and four of Hexagram 18 gives Dui, the Lake; taking lines three, four and five gives Zhen, Thunder. Thunder over Lake is Hexagram 54, which describes entering a household in a subordinate position, on terms somebody else arranged. That is a precise description of what the repairer in Hexagram 18 is actually doing. You did not choose the house, the arrangement, or the timing. You are the junior party in a situation set up before you arrived, and Hexagram 54 warns that pretending otherwise causes trouble. The opposite is found by reversing every line. The yin, yang, yang, yin, yin, yang of Hexagram 18 becomes yang, yin, yin, yang, yang, yin, which is Lake over Thunder: Hexagram 17, Following. Hexagram 17 is also what you get by turning Hexagram 18 upside down, so 17 and 18 are one of the few pairs in the Book of Changes where the overturned form and the line-by-line opposite arrive at the same hexagram.

The relationship between Hexagram 17 and Hexagram 18 is the more useful of the two structures. Hexagram 17, Following, describes going along with something, a leader or a custom or a current arrangement, and doing it well. Hexagram 18 is what that becomes when it runs unexamined for long enough. The traditional Sequence of the Hexagrams makes the link explicit: whoever follows others will surely have tasks, and so Work on the Decayed follows Following. Compliance is not the villain in this pairing. Time is. The nuclear Hexagram 54 adds the emotional texture the Judgement leaves out. Repair work under Hexagram 18 is rarely clean, because the decayed thing belongs to people who are still present, still attached to it, and frequently still in charge of it. The Marrying Maiden at the core of Hexagram 18 is why so many of these repairs stall on feelings rather than on facts.

What is the nuclear hexagram of Hexagram 18?

The nuclear hexagram of Hexagram 18, Work on the Decayed, is Hexagram 54, The Marrying Maiden. Lines two through four form Dui, the Lake, and lines three through five form Zhen, Thunder, giving Thunder over Lake. Hexagram 54 describes joining a household on terms arranged by others, the hidden position of anyone repairing an inherited mess.

How are Hexagram 17 and Hexagram 18 related?

Hexagram 17, Following, and Hexagram 18, Work on the Decayed, are a King Wen pair, and unusually the same hexagram results whether you turn Hexagram 18 upside down or reverse every one of its lines. The classical Sequence of the Hexagrams connects them by meaning as well: following others produces tasks, and following anything without review is what eventually spoils it.

What happens when all six lines of Hexagram 18 change?

When every line of Hexagram 18, Work on the Decayed, changes, the reading moves to Hexagram 17, Following. The shift runs from taking a spoiled inheritance in hand to going along with a new order, often read as the repair finishing and the repairer handing leadership to something that now deserves to be followed. It is one of the cleaner all-lines-changing transitions in the Book of Changes.

How does Hexagram 18 read for a decision, a relationship and work?

Hexagram 18, Work on the Decayed, answers a decision with repair, a relationship with an overdue conversation, and a work question with maintenance debt. For a decision, Hexagram 18 almost never endorses the new option. It redirects attention to something already in your hands that has been degrading while you weighed alternatives. The Judgement's crossing of the great water is not permission to launch something fresh; it is a demand to commit fully to the fix. For a relationship, Hexagram 18 points to accumulated silence rather than open conflict. Nothing exploded. A subject was avoided, a habit was tolerated, an imbalance was accepted for the sake of peace, and the tolerance itself is now the problem, which is exactly what line four names and warns against. For work, Hexagram 18 is the hexagram of the thing everyone knows is broken and nobody owns: the process kept alive by one person's memory, the account nobody has reviewed in two years, the handover that never happened. The Image insists the fix is not another rule. It is waking the people involved and building the standard that should have existed. In all three cases, Hexagram 18 assumes the reader has the standing to act and has been declining to use it.

The common thread across every application of Hexagram 18 is inheritance. Whatever the question, the hexagram assumes you are dealing with something handed to you rather than something you built, and it shifts the question from whose fault this is to who will handle it. Readers who argue with Hexagram 18 usually argue about authorship, and the hexagram is indifferent to authorship; its line texts absolve the parents twice over. The second thread is timing. Hexagram 18 rarely means act this instant, and it never means wait and see. The days bracketing jia describe an interval: enough preparation to understand why the thing rotted, a marked beginning, then attention sustained long enough for the repair to set. The third thread is company. Neither the Image nor line five imagines a solitary hero. The repair succeeds when other people are stirred into it and given something durable to hold onto, and it fails when one person quietly absorbs the entire mess and privately calls that responsibility.

What does Hexagram 18 mean for a decision you are weighing?

For a decision, Hexagram 18, Work on the Decayed, advises against treating the new option as an escape from the old one. The hexagram identifies something already yours that has been quietly degrading, and it makes commitment to that repair the condition of the supreme success promised in its Judgement. If both paths are genuinely open, Hexagram 18 chooses the unglamorous one.

What does Hexagram 18 mean in a relationship reading?

In a relationship, Hexagram 18, Work on the Decayed, describes damage caused by avoidance rather than by any argument. A topic was left alone, a pattern was tolerated, and the tolerating has now cost more than the confrontation would have. Line four states the outcome directly: continuing to accommodate what was spoiled leads to humiliation. The repair is the conversation nobody has been willing to schedule.

What does Hexagram 18 mean for a career or business question?

For work, Hexagram 18, Work on the Decayed, points to maintenance debt: the undocumented process, the neglected client, the inherited team with no standards. It is a strong signal for anyone willing to take public ownership of a mess, since line five shows the repairer meeting with praise. It reads badly for anyone hoping to leave the decay for a successor.

Frequently Asked Questions

What is I Ching Hexagram 18 in one sentence?

I Ching Hexagram 18, Work on the Decayed, is Mountain over Wind, and it means an inherited situation has quietly spoiled through neglect and is now yours to repair. Its Judgement promises supreme success for the repair, not for the situation, and it instructs the reader to cross the great water rather than manage the problem from a safe distance.

Which hexagram does Hexagram 18 change into on each line?

Changing a single line of Hexagram 18 gives: line one, Hexagram 26, The Taming Power of the Great; line two, Hexagram 52, Keeping Still; line three, Hexagram 4, Youthful Folly; line four, Hexagram 50, The Cauldron; line five, Hexagram 57, The Gentle; line six, Hexagram 46, Pushing Upward. With all six lines changing, Hexagram 18 becomes Hexagram 17, Following.

Is the I Ching Work on the Decayed hexagram about family?

Hexagram 18, Work on the Decayed, is about family more explicitly than almost any other hexagram in the Book of Changes. Four of its six line texts refer to what the father spoiled and one to what the mother spoiled, framing the reading as a child taking on a parent's mishandled business. The frame extends to any inherited responsibility.

What does Hexagram 18 say about timing?

Hexagram 18 sets its timing through the Judgement's three days before and three days after jia, the first of the ten heavenly stems. It calls for a period of diagnosis before the work begins and a period of supervision after it starts. Hexagram 18 does not reward speed, and its fourth line makes clear it does not permit waiting either.

Should I take on the repair Hexagram 18 describes?

Hexagram 18, Work on the Decayed, answers yes, with two conditions from its own lines. Line two warns against forcing anything delicate, and line three notes the cost of pushing too hard even where force works. Line one concedes real danger and still ends in good fortune. Only line four, which tolerates the decay instead of repairing it, ends badly.

What is the difference between Hexagram 18 and Hexagram 17?

Hexagram 17, Following, describes going along with a person or an arrangement, while Hexagram 18, Work on the Decayed, describes what that arrangement becomes once nobody has reviewed it for years. Structurally they are the same hexagram inverted and also the same hexagram with every line reversed. The Sequence of the Hexagrams links them by meaning too: whoever follows others acquires tasks.

Why is Hexagram 18 called the Gu hexagram, and what do the worms mean?

Hexagram 18 is called Gu after a character showing three insects above a bowl, the picture of a vessel left standing until its contents bred worms. In Chinese folklore gu also named a poison made by sealing venomous creatures in a jar until one survived. Both senses give Hexagram 18 its central idea: corruption growing inside a container nobody opened.