Stress may be defined as the response of the body to any demand. Whenever people experience something pleasant or unpleasant, we say they are under stress. We call the pleasant kind "eustress", the unpleasant kind "distress". People sometimes compare our lives with that of the cave man, who didn't have to worry about the stock market or the atomic bomb. They forget that the cave man worried about being eaten by a bear or about dying of hunger—things that few people worry about today. It's not that people suffer more stress today: it's just that they think they do. It is inconceivable (不可思议的) that anyone should have no stress at all. Most people who are ambitious and want to accomplish something live on stress. They need it. But excessive stress is by all means harmful. Worse, chronic exposure to stress over a long time may cause more serious diseases and may actually shorten your life. The most frequent causes of distress in the modern man are psychological—lack of adaptability, not having a code of behavior. So the secret of coping with stress is not to avoid it but to do what you like to do and what you were made to do, at your own rate. For most people, it is really a matter of learning how to behave in various situations. The most important thing is to have a code of life, to know how to live.