The superior physician intervenes before disorder has taken form, because once disease is fully present treatment is like digging a well after one is already thirsty or forging weapons after the battle has begun. Governing the body (and the state) by waiting for visible breakdown means acting too late.
Wood, fire, earth, metal, and water are assigned to organs, seasons, colors, tastes, emotions, and directions, so that each phase both generates one phase and restrains another in fixed cycles. Reading a symptom means locating it in this web and tracing which generating or controlling relation has been broken.
Health is read as the alignment of internal qi with external cycles of day, season, and climate, so that illness is understood as a mismatch between a person's internal state and the environment they inhabit. The seasons dictate how one should sleep, eat, and exert effort, and violating the season's quality breeds disorder later.
Yin and yang are not fixed substances but a relational pair whose relative proportion is always shifting; health is their continuous mutual adjustment rather than a static state, and either one in excess or depletion produces illness. Because the two convert into each other at their extremes, extreme yang gives rise to yin and the reverse.