Consider the children of the same parents that you know. Note that these children, reared in the same environment, still differ greatly from each other and from their parents. While you may have fun with Benjamin who is as old as you are, you find it difficult even to start conversation with his brother Joseph. To you and to most of your friends, Joe, who is usually quiet, is a puzzle. However, another brother Bong talks a lot and plays the piano very well. He makes you feel at ease, and people like him. Still, you would rather be with Ben than with either Joseph or Bong.
In our day-to-day lives we come in contact with many kinds of people. Some we like, some we dislike, and some, for whom we have no particular feeling about. But we must get along with all these people. It is impossible to associate only with those we like. If we are to get along with others, we must understand ourselves first. These are the reasons why understanding behavior differences, that is personality differences, is necessary.