Pot odds are not enough — you need implied odds to call correctly

Pot odds tell you the price of a call right now. Implied odds estimate what you will win on future streets if you hit. A flush draw with 9 outs needs ~4:1 pot odds to call. But if your opponent has a big stack and will pay off a flush, your implied odds make the call profitable even at 3:1 or 2.5:1 direct odds. Implied odds are what separate break-even players from winners.