It's good that you have enough self esteem that you do stand up for yourself and you are not just a push over where others learn they can walk all over you. Human beings ARE primates and tend to practice primate behaviors where they do test boundaries and compete in that if they can invade a boundary or find fault in others they can feel empowered. Human beings tend to be competitive in nature and this is very evident in all the competitive sports human beings partake in or gather to observe. Even in how we educate our young children revolves around competing in who gets the higher grade or who is the best at this or that. We actually teach the wrong way to develop what is considered "healthy self esteem" without realizing it. So, one of the things we end up producing at young ages is "stress" and "anxiety" instead of developing a personal sense of balance and pride.