The fourth line is the most crowded image in Grace and the most human. Legge's translation shows a subject looking as if adorned but only in white, mounted on a white horse and flying swiftly on, seeking union with the first line, while the third line between them pursues, not as a robber but intent on a matrimonial alliance. Everything is white, which is to say unornamented, and everything is in motion, and the whole difficulty of the line is that motion and plainness together look alarming.
The colour is the key to the ornament question the hexagram keeps asking. This line has stopped decorating. Horse and rider are both plain, and plainness offered as a serious approach can be misread, since an unadorned arrival gives an observer nothing to interpret it by. The third line, hurrying after the same union, is not a threat at all, but at speed and without ornament it is indistinguishable from one until it stops long enough to be understood.
A yin stroke correctly occupies this even position at the base of the upper trigram Gen, and it answers the first line across the span of the hexagram, the two of them joined in preferring the plain to the decorated. Between them stands the firm third stroke, which is why the approach cannot be direct. The line describes a genuine relation delayed by appearances rather than obstructed by anyone's intent, and it resolves the moment the appearances are read correctly.