I agree with whats above, but I take a different tact on things.
I believe my job at the poker table is to make money. To make money I want to make other players make mistakes. It's gambling and there is always the chance that you may lose a hand that you "shouldn't", so you need to attempt to make other players make bad choices. The more times you can make your opponent make a bad play will only increase your chance of making money.
This is why I don't understand about getting mad at 'bad beats' and how people freak the hell out on stuff. If you did your job right and made your opponent make a bad play, then how can you get upset. Sure it's a little frustrating, but so long as you do your job right, it all works out in the long run.