Psychologists believe that self-esteem is formed through social comparison. Everyone needs to know his own needs and his position in the group and society, so as to realize his own value. Sometimes, we can know ourselves through some objective reference standards, such as blood pressure, pulse, temperature and other observable indicators to understand our health. But many times, there is no such objective standard for reference, and we can only evaluate ourselves by comparing with others. For example, people cannot estimate their height and weight. People can't answer whether a person who is 1.80 meters tall is tall or short, because there is no objective standard to refer to. In some places, this person may be only a medium; But in other places, this man may be a giant. A typical example is that most freshmen will have this experience: in high school, everyone is smart; But after they went to college, they found that they were not so outstanding, just ordinary people.