Is there a "wall" for mental work?

[Bob]

Just like exercise?  You hear marathon atheletes having a "wall" they will hit.

It must also be true that doing a lot of thinking or a lot of projects... You come up to a similar "wall."

But if runners can manage overcoming that wall... then anyone else doing their own work, whatever that is, must be able to manage overcoming their own wall too, right?