Where the first line sought union at the open gate, the second line withdraws it into the walls of one's own clan. Legge's translation renders the image as fellowship with kinsmen, confined and therefore a cause for regret, a striking judgment given that this line is also, structurally, the very center the rest of the hexagram is built around. The text does not deny the line's importance. It warns instead that even the hexagram's most central line can fail its own theme if the union it forms narrows to blood relation rather than staying open to the wider fellowship the Judgment demands.
This is the sole yielding line in a hexagram otherwise built entirely from firm strokes, and Chinese commentary has long treated it as the hexagram's ruling line for exactly that reason: every yang line in Fellowship with Men is read as seeking union with this one yin line, much as a court seeks the favor of its single minister of standing. Centrality and correctness both belong to this position, an even place rightly held by a yielding line, which is precisely why the text singles it out for caution rather than praise. A ruling line that turns private squanders the very authority its position grants it.
Placed at the second step of the lower trigram Li, closest of all six lines to the intimate and enclosed, this line embodies the risk the whole hexagram exists to guard against: that fellowship, sought too close to home, curdles into faction. The regret named here is not failure but a narrowing that a line of real consequence can least afford.