I am Godlike... in my own eyes of course!
If its a familiar genre I find I tend to blow through games on hard (so I'll normally jump right to Hard for FPS games for example) but if its something new I tend to devote extra time to learning the new mechanic(s) involved in beating the game.
But beat it I will. A game has to be horrible for me to not complete it - and I try to avoid buying horrible games in the first place.
Try to be reasonable... its easier than you think...