I want to second this. This is a prime example of how self-image can be very useful. I myself do something similar. Yes, I would say that it is very possibly at least partially a placebo effect, but that doesn't matter, because what I care about is getting the benefits, and whether the benefits come from the placebo effect or a more direct effect, in either case I benefit. (That said, I do think that at least some of this effect does come from the self-image narrative change as discussed in this post, and the effect is not entirely a placebo.)