This can be hard to understand from a habitual reactionary manner of being. I should have qualified that to say that insecure/immature people will often react angrily to an untrue defamatory statement, because they think it's all about them, and they don't know who they are and are not. Adults who know who they are and are not know better. They know that getting upset is what the other person wants, and they also know that getting upset will not benefit either of them. Say someone calls me a cheater, and I know I didn't cheat. That other person isn't calling me a cheater because I'm actually a cheater; they're doing it to try and meet some need of their own. Perhaps they believe that if they ever "lose" there is something "wrong" with them. So instead of accepting that they actually lost, and understanding that there is nothing wrong with "losing" sometimes, they deny they lost, and they blame someone else or "the system." It's all about them, not me. An angry reaction from me only feeds their denial and their attempt to make others responsible for their own thoughts and feelings.