The first reason is that a trustful friend could be the most helpful person inside school or work. For example, let's consider that you've gotten into big trouble because your teacher has misunderstood a situation. If one of your friends is reliable, he or she can at least support you and explain the situation to the teacher. This act cannot be done if a friend is smart or funny. Through your trustful friend, you will be able to feel more comfortable than anyone else inside the school or work.