It feels like the same kind of reason that you need to be gentle with your body after running a marathon. I could try to be more specific about what might be going on that makes it difficult to keep it up, but the point is that it seems to be a fundamentally difficult to remain unfatigued and if you don’t slow down when fatigued you’re not going to move very well and are likely to break something.
Are you asking more “why can’t you mentally run unlimited marathons in a row without slowing down” or more “what damage do you risk doing when continuing through ‘mental fatigue’ that makes it something you have to heed?”?
It feels like the same kind of reason that you need to be gentle with your body after running a marathon. I could try to be more specific about what might be going on that makes it difficult to keep it up, but the point is that it seems to be a fundamentally difficult to remain unfatigued and if you don’t slow down when fatigued you’re not going to move very well and are likely to break something.
Are you asking more “why can’t you mentally run unlimited marathons in a row without slowing down” or more “what damage do you risk doing when continuing through ‘mental fatigue’ that makes it something you have to heed?”?