Discipline insisted on plainly, before a single engagement, is this line's whole subject, and its placement may be exactly why. A yin stroke occupies an odd position, an irregular placement by the standard rule that assigns firm lines to odd places, and a beginning that lacks inherent firmness needs deliberate structure imposed on it rather than trusting to its own natural strength.
Positioned at the foundation of Kan, the trigram of danger the whole campaign is entering, the line has nothing yet to react to, only a condition to establish in advance. When this line changes, the bottom stroke of Kan becomes firm, turning the lower trigram into Dui, the joyous lake, while the upper trigram Kun remains fixed above.
The resulting hexagram is Number 19, Approach, earth over lake, an image of two firm lines advancing steadily beneath four yielding ones, a rising influence gathering strength as it goes. The pairing fits: an army whose discipline is properly set at the very outset does not merely avoid disaster, it builds toward a genuine and growing advance, exactly the kind of steady approach the resulting hexagram describes, rather than a force that must fight simply to hold its ground. That the transformation replaces one kind of movement with another rather than simply erasing the army's original discipline suggests the hexagram treats good order as something that redirects rather than disappears once tested.