This is a good question. In Sklanskey, Miller, Malmuth book they advise that if you have a positive EV along with sufficient Pot Equity, PO, IO then you must play "regardless of the outcome." It is the long term game you are desiring to conquer, not necessarily one hand in one game. They say the only way to do that is by the manner stated.

Now given, this is in limit poker not NL. At any rate, it takes as much nerve to lay down a good hand as it does to bet one, maybe more... It is the difference between knowledge and discipline. For my money discipline is more profitable in the long run.

Most times it is not a question of wheather you have the balls; do you have the nuts?!