But when you're getting a lot of action, and the flop doesn't look real drawy, it's sometimes a hand you want to think about backing away from.
When there aren't a lot of draws showing on the flop you can be pretty sure that any action represents a strong holding.
Let's say you have a 5h7h and the flop is 57J, rainbow, you bet and there's a raise and a re-raise. That's pretty heavy action. What do they have. If there was no raise preflop you might want to eliminate JJ or AJ (you might not want to eliminate those possibilities, but let's just do it for this example). That leaves Jx, say J7-JK, 77, 55, 57, or 86 as possibilities for the first raiser. The second raiser probably doesn't have a single pair, he probably has one of the stronger possibilities, or a straight draw. Running pokerstove we get a 36% equity for bottom two pair in the 3 way pot.
That makes it plus EV for you on the flop, but that's if the hand ranges I'm assuming are accurate. It could be that you're a little better than 36%, it could be a little worse. In any event it's close to a wash for you if the action is very heavy and the bets make the dead money already in the pot insignificant. If the money left is deep it could be a negative implied odds situation for you too. What are you going to do if a 9 falls on the turn? A Jack?
In limit poker, if you're estimate is that you're ahead you should stick it out almost every time. But in no limit you sometimes need to think in terms of what the finance people call risk-adjusted return. Sometimes in no limit a plus EV situation isn't really plus EV once you make a risk-adjustment. That's a topic I need to cover in some detail at mathandpoker.com one of these days. But, for the most part the thing to keep in mind is that if the EV edge is small and the risk is large you should often give it up in no limit, wait for a better situation.