The mindset that brings unlimited willpower

Interesting. On the other hand, this isn't about willpower per se. That's onlt an example. It's about identity. You are - or can be - what you identify to be. I've seen the power of identity mentioned in various books including books by: Annie Duke, Michael Easter, Nir Eyal, and (I believe) James Clear. Others? Anyone?

At a more pop culture level, it's a version of Ted Lasso's "Believe".

Fwiw, I've distilled this all down to a single heuristic:

Belief drives behavior.

Another example of confusing cause and effect. Perhaps the people with the view that 'ego depletion' was a thing, had that view because of personal experiences.

If so, then all we've shown is that their clever quiz detects people that suffer from limited willpower. Which is a valuable result, but not worthy of the overheated claims in this article.