I think understanding that bad beats happen, and learning to stay calm even when things are going against you is one of the most important skills in the game.

Sure if you make a bad play there's nothing wrong with dwelling on it (after the game not during!) but it's essential to keep your head even when the cards are laughing at you.

I find I play much better if I have a break after every game, win or lose. I can think about how I played and what mistakes I made, then dust myself off and return to the tables with a clear head.