It is said that a series of chemical changes occur in the brain from acquaintance to acquaintance to love between the opposite sex, which is very similar to the courtship of other animals. The stimulation of the opposite sex’s voice, appearance, smell and other signals will cause the human hypothalamus to produce a kind of endorphins, which will act on the limbic system of the human brain, thus producing a pleasant emotional response, further producing the so-called passion. However, continuous stimulation by the same stimulus source leads to a gradual decrease in the release of these endorphins until they are no longer released. In humans, this release process lasts only for about 18 months, after which it is repeated in the brain when a new source of stimulation, i.e. a new person of the opposite sex, appears. Pure love only lasts for about 18 months. So what should two people who fall in love after 18 months do? Since pure love only lasts for about 18 months, wouldn’t the divorce rate be 100%? However, this is not the case, why? Let’s shift our perspective and treat this theory as a myth for a moment and look at the issue from a different perspective. As we know, human love is still a social emotion, subject to social constraints, we can not love whoever we want, today we like him and marry him, and tomorrow we like someone else to divorce the original spouse, and then establish a new family. Few people do this, why? That is because in the process of individual growth, we are constantly undergoing socialization, and in the process of socialization, some social norms, ethical codes, and moral concepts are gradually internalized to form the superego component of our personality, which supervises our behavior, so that our behavior remains within the scope of social permission, which follows the “principle of the highest good “. The other component of the personality, the ego, is the underlying motivation for individual action and follows the “pleasure principle”, the need for immediate gratification. The ego, which unites the two, follows the “principle of reality,” satisfying the needs of the ego while complying with social norms.