something i wanted to put down in words
If you are a good hand reader and you can't really put villain on a hand/range, it's probably because his range is wide. in holdem, most hands cant withstand bigtime pressure. So that's what you need to apply when their range is wide.
if you are a good hand reader and you can put villain on a very narrow range, perhaps even one exact hand, that's probably what he has. you should act accordingly even if that means making a 'big fold' which people genuinely feel is bad in shorthanded aggro games, and that probably has something to do with the fact that a lot of people are so nitty that they dont WANT you to be making those folds because they always have... uhh... i dunno.