[ELI5] Why can’t we concentrate nonstop? Why do we need breaks?

Question

EDIT: I mean productive work such as learning.

In: Other

Answer 1

For the same reason you can’t run forever.

Thinking is energy intensive, we dedicate a large amount of calories to our brain and focusing, concentrating and thinking increases that energy burn.

Eventually you tire out and require rest and to restore your energy reserves.