I really like the way Adrian Sullivan breaks down mistakes in this article. I am often concerned with playing the best game I can play. I don't expect those games to be flawless, rather, I endeavor to make the most correct series of decisions given the information I have at the time.
And this is a far more forgiving way to look at the game, I think. Because Magic is a game of incomplete information, one can never be assured that they are making the correct play. Luck does play a factor and sometimes, you (or your opponent) just gets lucky.
Hell, I've won games because I made a mistake. That is about as backwards a system as I can think of.
Although the potential commentary it makes on life at large is damn near irresistible. Still, the goal of playing the best game I can play is worth more than playing a mistake-free one, I think.