Against a hexagram given over to mood, the second line offers stone. Legge's translation calls its subject firm as a rock, says he does not wait until the end of the day, and attaches good fortune to firm correctness. Two virtues are combined in a single stroke, and they are usually thought of as opposites: immovability, and speed. The line is unmoved by the enthusiasm around it and, for exactly that reason, sees where the enthusiasm is going before anyone caught up in it can.
Yielding in an even place, central in the lower trigram Kun, this is the only line in Enthusiasm that is correct and central at once. Kun is the receptive earth, and the second position is where its stability concentrates. The classical reading attached to this line concerns perceiving the first faint indications of a thing while it is still forming, and the reason such perception is possible here is structural rather than mystical: a line that is not being carried along can still see the current.
Not waiting until the day is out is the practical half of the line. Perception without timing would be commentary, and the text is not describing an observer. Having read the situation early, this line acts on the reading early, before the mood has hardened into a position that would be expensive to leave. Firmness and quickness turn out to be the same virtue seen from two sides, and the good fortune promised belongs to holding both.