Similarly, I'd guess most players think they're winners because they're better than average. No, not really. Your profit comes almost entirely from very bad players. You win because you extract well from them. Grinding out a small edge against average/decent players doesn't even beat the rake.
I don't question myself so much about gambling it up in marginal spots any more. It's possible that I'm making some -EV moves in those spots. However, overall my game is more +EV than ever. How can that be? Well, it could just be variance, or it could be that making a little -EV move once in a while is actually +EV, because it gets you action, or makes people stop bluffing you when they see you make a call with ace high. The truth is all those little factors are very hard to count, so making a little -EV move once in a while is not really something to worry much about.