Most of your result is decided before the flop
The hands you choose to enter a pot with put a ceiling on how much you can win and a floor under how much you can lose. Play too many weak, dominated hands and you spend the whole session making tough decisions from behind — that single leak costs beginners more than any misplayed river. A tight opening range built around your table position keeps you out of those spots before a flop is ever dealt — you're simply choosing better fights than the players stacking off around you.