I never heard of ego depletion theory, so I did a Web search. I found this article saying that the theory may be completely bogus.

As to what I think of it, it seems kind of wacky. It is like the latest craze in educational theory of grit. This is the idea that education is not meant to be enlightening or enjoyable. What counts is the ability of the student to stick with it no matter how poorly the material is being presented.