There is a near-consensus that diet is more important than exercise, at least for aesthetics.

I think this idea suffers from a similar problem as that suffered by ‘calories in calories out’: although it might be true in some idealized sense, “calories out are endogenous to what is eaten”.

Here, diet-in-reality is largely determined by ’the kind of person you believe yourself to be.’ Exercising more makes it easier to see yourself as the kind of person who takes diet seriously, and therefore improves diet. The reverse doesn’t feel true.