[OrianasDaad]

A flush draw is a good example. You have a 19.6% chance to improve to a flush.

Let's say the pot has $100 on the turn, and your opponent bets $50. You don't have the odds to call with a flush draw:

(.196 * 150) + (.804 * -50) = -10.8.

You lose $10.8, according to pot odds.

If you figure that you can make more than that extra $10.8 when you do make your flush, then a calling is OK.

At least that is my interpretation of it.