This Chapter is a dialogue from the Yellow Emperor's Classic of Internal Medicine, exploring the causes of illness. Shao Yu, a physician, explains that illness arises not solely from external factors like wind and cold, but also from individual vulnerabilities. He uses the analogy of different types of wood reacting differently to weather to illustrate how internal constitution affects susceptibility to disease. Shao Yu describes physical indicators that correlate with a predisposition to various ailments, such as wind conditions, emaciation, chills, fever, and obstructions. The discussion emphasizes both the external triggers and the internal predisposition in the development of disease.