As a divinatory line, six at the first place of Before Completion reads within the hexagram's overall concern with progress and success, like a young fox that has almost crossed the stream when its tail gets wet, so there is no advantage in any direction yet. The line occupies a place that does not match its own nature in the classical doctrine that odd places favour a firm, yang line and even places favour a yielding, yin line. Its own text, that the tail immersed, a case for regret, is the particular fortune assigned to this one stage of the situation, not to the hexagram as a whole.
The first line corresponds by classical convention with the fourth line, and the two correspond here, since one line is yin and the other yang. Read together with the trigram it belongs to, Kan in the lower position of the figure, the line marks the opening of the situation, before the trigram above it has any part in the reading, one stage in the six stage movement the hexagram traces from its first line to its last.
A change at this line, from yin to its opposite, is the mechanism the tradition uses to move from one hexagram to another. Flipping the first line of Before Completion turns Kan into Dui while the other trigram, Li, stays as it is, which yields Before Completion's changing partner, Opposition (King Wen 38), the hexagram this line is recorded as transforming into.