Originally Posted by LawDude
One other situation you should be draws is where, even if you have no fold equity whatsoever, you have a big enough draw that you have pot odds to justify a bet.
For instance, suppose you call a pre-flop raise from a nit (raising range, AA and KK) with 9c8c. The flop is 7c 6c 2h. Well, at this point you are actually a favorite (usually about 55 percent) to win the pot, even though you are currently "behind" (in the sense that you don't have a made hand and your opponent does).
That's a really specific example that's pretty unrealistic and just generally rare. Note that if same situation happened, but the flop was 8s 7c 2c and you truly had NO fold equity whatsoever betting would be wrong because thanks to rake and possible backdoor flush draws for villain you have slightly less than 50% equity.