Confucius mentioned the "three precepts" in the Analects of Confucius Ji Shi, that is, "a gentleman has three precepts: when he is young, his blood gas is uncertain, so he should be careful; It is also strong and bloody, and it is fighting; I am also old, my blood gas is declining, and I have to quit. " In other words, people should keep in good health according to different physical, age, physiological and psychological characteristics. If you are a teenager and your body is still immature, be careful not to get married too early and have too much sex. If you are in the prime of life, you are strong, strong and angry. Remember not to fight with others, lest you hurt others. When you are old and weak, you should look down on fame and fortune and stop pursuing anything deliberately.