to put that in a little more detail... if you have a villain who is let's say 34/18, you're on the button with like ATs. Against this kind of villain you would be ahead of his opening range. Same position same hand you have a villain who's 8/8. If he raises you are most likely behind his range. Download pokerstove if you haven't already and get familiar with it and you can use it to get an idea of how much equity you have preflop against certain villains opening/raising range. Once you mess with it for awhile you will start to get a feel for it and should be able to figure it on the fly