[Jimbobobb]

Let's make the math super simple.

Monkey: AA

Board: A B C

On the turn, you have 3 B's and 3 C's and 1 A that can give you a boat/quads. 7/47 which is approx 14.8%

Turn: A B C D

On the river, you have 10 outs to a boat or quads (3 B's, 3 C's, 3 D's, and an A) whish is 10/46 or approx 21.7%

14.8 + 21.7 let's just say is around one third of the time you'll improve to a boat or quads by the river. That means odds are good that you'll win this pot one third of the time. Well, there are 3 people willing to call any bets you make. Like EdSchurr said above me, the situation is clearly +EV to raise, since you will get back in the long run 1.38 bets per bet that you make in this situation. What you're doing here is pushing your pot equity edge. On that flop you can say 'I'll win this 33% of the time'. That's much more than your fair share against a field of 3.