I think often, the longer you hang around people the more of their flaws you will see because that is just human nature isn't it? No matter how well you try to hide it, sooner or later people will know? And I suppose for us it is about learning about how to be less sensitive about what people may think about us, but still sensitive about whether our actions are considerate towards them.
However, human nature can be such that :
If we stick with people that we cannot stand long enough, We can "kill" them.
Okay I'm kidding, this is exaggerated, but you get the idea. It is just what humans are capable of and more often than not, we become very bitter in our hearts toward people we don't like.