in heads up its different. it completly drains momentum from the aggressive player. Your thinking goes from i was good on the flop but those over cards on the turn and river look scary... Also you never know when they are slowplaying because it's been what they've been doing the whole match so they get extra bets on the flop and the turn and then put in a big bet on the river...and they'll also have enough sense to get away from hands there probably beat at.
anyways like i said think before you write..