This lesson was important to me because a couple of times, when someone didn't treat me the way I wanted to be treated, I blamed myself and said, "I must be a very bad person who can't get along with people and can't handle friendships. Because X gets along fine with everyone else and they all think X is great, but X and I don't get along at all." However, when I looked closely I saw that X acted pretty much the same with everybody, or at least everybody who was like me (some people treat their close friends different from their distant friends, or women different from men), and it wasn't me at all, it was just how X was. Once I realized that, I was able to stop blaming myself for whatever awful thing X did to me. Although I would usually get angry at X if they had somehow insinuated that the fault for us not getting along was mine, or that I was a bad or defective person because I refused to play along with their sick (to me) little patterns.
I'm continually amazed by the types of behavior that other people will tolerate or even welcome, when I hate it myself, but I'm sure other people are sometimes taken aback by what I can tolerate or even find useful.