In the concept of traditional Chinese medicine, the human body is produced and formed by amphoteric substances represented by yin and yang. So Su Wen said: "The foundation of life lies in Yin and Yang." He also said, "Yang gives birth to Yin, while Yang kills Yin and hides. Yang is shaped by qi and yin. " It is also believed that human beings are the unity of opposites of Yin and Yang, and they must always maintain a relative balance between Yin and Yang in order to live a normal life. Therefore, Su Wen said: "Yin people are good at hiding essence, while Yang people are honest ... Yin Pingyang is the secret, and the spirit is the rule." If the yin and yang of the human body are out of balance for a while, it is bound to get sick. The purpose of treating diseases is to balance yin and yang. Therefore, Su Wen also pointed out: "Yin wins Yang disease, and Yang wins Yin disease; Yang wins is hot, and Yin wins is cold; Heavy cold is hot, and heavy heat is cold. ..... check its yin and yang, not rigid and soft, yang disease cures yin, and yin disease cures yang. " Since the human body is the unity of opposites of Yin and Yang, it can cure diseases and prolong life by keeping the relative balance of Yin and Yang.

Because everything in nature is the unity of opposites of Yin and Yang, and it is produced by bisexual substances represented by Yin and Yang, the human body should not only keep the balance of Yin and Yang in the body, but also adapt to the nature of Yin and Yang. Therefore, in Su Wen, it is repeatedly said that "nourishing heaven and earth, grasping yin and yang", "harmonizing yin and yang, adjusting the four seasons", "harmonizing heaven and earth, following the eight winds" and "governing heaven and earth like the sun and the moon". Who can adapt to natural conditions and keep the balance between internal and external environment in this way can achieve the goal of longevity and health in health preservation and disease prevention.