The following ideas were taken from Reinventing Yourself: How to Become the Person You've Always Wanted to Be by Steve Chandler, an amazing and easy read.
Basically, what it says is that there is no such thing as personality, only choice. You can be anything you want. You can be confident. You can be joyful. When someone does something inconsiderate, you can choose to become angry or let it slide.
Please realize this is only a short summary on the subject, but think about it. If you get and angry and say, "Oh, that's just the way I am." then isn't personality just a reaction due to precondition? And if this "personality" is just a reaction, then how much of our lives do we spend reacting?
I'm not trying to scare anyone or hurt feelings, but really, it's all choice. We are all very talented, very capable beings. We should choose to believe that.