Can someone show me the math for this..

I want to understand why value betting in a situation where your against one or more opponents is correct - even though they have odds to call you.

For example, On page 30-31 of SSHE:

"Say you are playing $2-$4, and the pot is $44 on the turn. You have top pair, and your lone, loose opponent has four outs to beat you. If you bet $4, then the pot will eb $48 (the original size plus your bet), and your opponent will have pot odds of 48 to 4 or 12 to 1. Since that is more than the break even point for his draw (10.5 to 1 for four outs), he can call profitably."

What I want to know is that since he is making a positive expectation play by calling your bet, you must be making a negative expectation play by betting into him. I understand in poker that with every decision you want to MAXIMIZE your expectation. I think I'm missing a basic concept, and if anyone could show me why value betting here is right along with the math I would greatly appreitate it.