Normal humans have a fairly limited set of true desires, the sort of things we see on Maslow’s hierarchy of needs. Food, safety, sex, belonging, esteem, etc. If you’ve become so committed to your moral goals that they override your innate desires, you are (for lack of a better word) a saint. But for most people, morality is a proxy goal that we pursue as a strategy to reach our true goals. Most people act a culturally specified version of morality to gain esteem and all that goes with it (jobs, mates, friends, etc).
Your true desires won’t change much over your lifetime, but your strategies will change as you learn. For example, I’m a lot less intellectual than I was 30 years ago. Back then I was under the delusion that reading a 600-page book on quantum mechanics or social policy would somehow help me in life; I have since learned that it really doesn’t.
Clearly I’m what the OP would call a cynic, but it misunderstands us. I’m a disbeliever, sure, but not a coward. I know well that peculiar feeling you get just before you screw up your life to do the right thing, and a coward wouldn’t. I just no longer see much value in it. As Machiavelli said, “he who neglects what is done for what ought to be done, sooner effects his ruin than his preservation.”
The true test of a saint is this—if doing the right thing would lead to lifelong misery for you and your family, would you still do it?
Fair enough, but I’d still say that most people do “good” (by which they mostly mean culturally approved things) as a strategy to achieve some more basic end. In support of this proposition, I’ll note that “good” is defined by different people in different ways that all generally correlate with cultural approval in common cases but strongly diverge in matters of basic principle. See Scott Alexander’s: The Tails Coming Apart as Metaphor for Life.