Yes. Sometimes you'll make the best hand postflop and sometimes they'll just fold to your cbet. Either way, you have position so you'll be winning way more than you'll be losing if your steal attempt gets called.
All I was trying to say is that if you run your numbers with the formula Stu used above and see that you're not making an immediate profit because people aren't folding quite enough, you don't necessarily need to decrease your ATS% or the size of your steal attempts. You'll still be making heaps of money when you attempt to steal.
Its only an issue if its way under what you need.
You make it up for c bets on the flop and then the turn.
A better way of looking at it is that you are not trying to show an immediate profit from stealing (although against some you will) but what you are doing is reducing the average cost of seeing a flop. You also off set some of the burden of the blinds.
people dont tend to play back with a significantly wider range to a smaller bet than a bigger bet so by betting smaller you risk less and thus profit more. You also do interesting things to the 3bet size.. meaning that you can call a 3bet with a wider range as you have position and its a smaller 3bet size. OR the villian continues to make big 3bets which mean that he nees to be successfull more often than if they were smaller so when you have a hand, you profit more.
I.e. if he 3bets to his normal standard size then you can fold more because when you do get a hand you make more money back when you 4bet/flat.
if he 3bets to a smaller size then you get better
odds on a call and can widen your flatting range *a bit*