I have chosen a poor example and formulated my question in a misleading way. I do not work physically and I am more likely to lack willpower when I am mentally tired even when it is related to other things than physical exercise - for example I am trying to reduce my sugar intake and I am more likely to just give up eat some chocolate after a tiring (mentally) day. That is what I thought was the kind of obvious thing - that when people are mentally tired they tend to just watch a movie instead of originally planned language learning. This is what's disputed?

I am asking because either I do not understand the ego depletion concept or something that seemed really obvious to me is disputed, which would surprise me.