 There are two psychological reasons as to why this seems to happen, the first being social pressure and the other being the set of assumptions people tend to make about those who are similar to themselves.Students are often socially pressured to form friendships depending on the person's age, gender, social class, or racial-ethnic background.Parents and other adults involved in a child's life can also have a large influence on the friendships that children choose to have, this being because they teach children to select "appropriate" friends who won't pass on bad morals or inappropriate traits.