If I were to write an intellectual biography of Tyler Cowen, one topic I would cover would be free variables vs. set points. Something is a free variable if we can set it at whatever level we choose. Something has a set point if it tends to revert to a particular level no matter what we choose.
Seth Roberts' view of dieting is that people have a natural "set point" for weight. Unless you change your set point, you cannot permanently change your weight--you can only yo-yo around the set point. Tyler is a big Seth Roberts fan.
On Marginal Revolution, Tyler once cited (and said he wished he had written) a paper which speculated that one's self-control is governed by a set point. Exercise more self-control in one area and you will have less somewhere else. Try to cut back on gambling and you'll end up going off your diet.
In his book, he cites Dennis Robertson's article on "What Do Economists Economise?" As I recall, Robertson viewed the amount of altruism as limited, so that if economists proposed using markets for something that previously required altruism, then more altruism would be available elsewhere. To me, this says that if we paid blood donors, the altruism of today's free donors would be shifted somewhere else. Lots of people would argue something close to the opposite.
On his secret blog (the link does not take you there--it takes you to the post that says what you have to do to get access), he speculates that individuals might have set points for self-regard, so that if you praise them they feel insecure or if you doubt them they feel reassured.
He also speculates on the implications of a set point for dogmatism. If you are going to be dogmatic to a fixed extent, the more dogmatic you are about, say, religion, the less dogmatic you will be about politics or economics.
On the other hand, Tyler often suggests practicing exercising virtue. If you advocate practice, then your metaphor is of a muscle that gets stronger through use, rather than of a body thermostat with a setting. If you do a search for "self-control" on Marginal Revolution, you will see posts that are consistent with the muscle metaphor as well as the one quoted above that is aligned with the thermostat metaphor. My guess is that Tyler is not committed to either one.
The implications of the thermostat metaphor and the muscle metaphor tend to be quite different. So it is probably worth investing some effort in trying to verify empirically which one best fits a particular behavior or cluster of behaviors.