1. If your current equity + future equity is better than your pot odds
by future equity I mean folding equity/implied odds on later streets
2. If you get called by worse more times than you get called or raised by better minus the EV you lose when you get bluffed out of the pot with a bluff raise
3. If your folding equity plus future equity is better than the amount you're risking

two main elements:
equity in the hand
pot odds (or pot percentages)