Or here's another way of looking at it. You have 67s and you believe your opponent has two overcards. You're a 60-40 dog. Lets say he is going to see every hand to the river, like the typical low limit donk, but you can read him and will sometimes fold when beat. You believe when you win you'll get 3BBs, and when you lose, you'll get away cheap and lose 1.5B. Your EV is 0.4*3 + 0.6*-1.5 = .3. Now when he has iffier holdings and your fold equity is factored in, its even better.

The problem here though is that you rarely get a donk in isolation. Raising in this spot at a .25/.50 table at party is trouble because both the blinds are going to call and three people are going to see the showdown. 67s can still be played profitably, but K4s has to be more picky.

To me good post flop play is maximizing your hands that are likely favorites and minimizing your losses when you are likely beat as someone said above. Realizing how to use the Check Raise properly to decrease opponent drawing odds, raising straight and flush draws for value in multiway pots, knowing when to just call a bet to allow overcalls are just a few of the things that can help a player to maximize the pots they win. Taking into account factors such as who raised preflop and how does his position relative to mine affect the way that I should play a certain hand according to the strength/weakness of my hand.

Playing at a good versus world class level doesn't in my opinion involve the ability to play alot more hands for profit because the majority of those very mediocre profitable hands show such a thin profitable margin over time that it just doesn't make that much difference. The big difference in the two simply come from doing those above listed things well post flop, excellent table/seat selection and never going on tilt.