The Importance of Knowing Your Opponent's Main Hand

When a player finds themselves holding a flush draw on the flop and they're facing a bet, it is not often the case that you can just say, oh, clearly that player has top pair. The only way I can win this pot is by hitting one of the nine outs. That's where a lot of the value of calling with the flush draw comes from. And that's why it's not terribly valuable to bet into the flush draw.