Actually thinking about, we can use your example.

You are dealt AA, you bet big and get 1 caller.

Flop is 5 8 9 rainbow, opp bets into 1/5 of the pot.
I would either assume he has hit his set, has TT - KK, or an overpair, (all strong hands since he called your bet big).

Now if you just looked at pot odds vs a set, you should fold, but he could just a easily have KK and bet strong like that on the flop. Which is why hold'em is such a complex game.