The fourth line describes the hexagram's most isolated position. Legge gives the subject bound in chains of ignorance, with occasion for regret. Unlike the earlier lines, which show ignorance being actively corrected, tolerated, or warned against, this line shows ignorance left entirely alone, with no teacher nearby to offer either firmness or patience, and the result is confinement rather than growth.
This line opens the upper trigram Gen, mountain and stillness, and its position at the foot of that trigram marks a place cut off from the lower trigram's instructive activity, water no longer reaching the ground it once watered. Chinese commentary reads the chains here not as punishment imposed from outside but as the natural consequence of isolation: folly given no correction and no company does not resolve itself, it hardens into something more fixed and harder to loosen.
The line's counsel, read through commentary tradition, is a warning about the danger of leaving any pupil, or any untaught impulse, entirely without guidance. Where the first line showed correction and the second showed patience, the fourth line shows what happens in their absence: not a dramatic failure but a quiet stagnation, regret arising simply from time passing with nothing done to answer the ignorance the line began with.