because after the flop you don't!! but it's hard to see how stuff like 2nd best trips on a fairly raggy board after the turn are not ahead as you aren't putting opponent on Aces and how can you read them as on 35.
on an A 2 4 9 board (no flush) with pocket 9's, could you find a fold to a re-raise all-in from a UTG caller to your pre-flop raise to 4BB's?
Therefore I'd rather get hands like 3-5 out of the equation pre-flop.