Chapter 40 states it flatly: reversal is the movement of the Dao. Anything driven to its extreme turns into its opposite — the moon fulls and wanes, the hard breaks and the soft endures, an army at its most confident is about to be beaten. The practical counsel is anti-maximising, which is unusual: do not seek the peak, because the peak is the beginning of the descent. This is why the text keeps recommending positions that a Chinese reader of the period would have read as humiliating — the valley, the female, the low ground, the infant, the uncarved block, water, which benefits everything and settles where people disdain to be. The same logic underlies the yin–yang diagram, in which each half already contains the seed of the other, and it is the theoretical backbone of Chinese medicine, strategy and dynastic historiography alike.