It goes along with assessing the pot amounts, but starts even earlier. If you're dealt a hand full of nothing - fold! If you're not bluffing, why put in any more money than you have to when the odds are against you. The reason most people stay in on a bad hand? 'Because it's boring to fold and wait for the next hand.' That's not something you'll ever hear a professional player say.
The exception to the rule is the occasional bluff. It's still not wise to stay in without a decent hand if someone else has initiated the raising and appears to have something. But, if you never put any money on the table without having 4 of a kind first, the players will eventually figure it out. When that happens, the pots will be small on your winning hands because people will know when to fold.