"I'm a loafer with a dead-end job in real life; why can't I play a hero in a fantasy game?" I've heard comments like this fairly frequently from gamers with whom I've played, over the years. Aside from the self-esteem issues implicit in the comparison, there's a fairly good reason why not every player-character is going to be a hero.
Heroes have to beat something. Overcome some sort of challenge. You know, win.
But for that win to have any meaning, there's gotta be uncertainty. The chance of losing. Which is why I've always said that player-characters in D&D (and frankly, any RPG) are not heroes when they are created. They have the chance of becoming heroes.
I was reminded of this when I read Dan of Earth's Simple Comparison. Nicely put, Dan!