The second line describes where an attachment comes from rather than what it obtains. Legge's translation shows the subject seeking union as something moved from within, from the inward mind, and promises good fortune to firm correctness. The small commentary adds the decisive qualification: acting this way, the line does not fail in what is proper to itself. Union is not treated here as a surrender of one's own standing but as an expression of it.
Central and correctly placed in the lower trigram Kun, this yielding line answers the single firm line in the fifth place directly, the classical correspondence between a soft second and a strong fifth. That correspondence is what allows the line to attach without diminishing itself. It is not reaching upward out of weakness, and it is not being drawn by pressure or by the crowd; the movement begins in its own settled conviction and finds its proper object already waiting.
Set against the first line's untested sincerity, the second marks the point where good faith becomes an actual relationship, still early, still unproven in circumstance, but grounded in something the line genuinely holds rather than in what it hopes to gain. The whole force of the line rests on that interior source. Holding Together, in this reading, is worth nothing when it is only conformity, and everything when the one who joins does so out of what is properly their own.