This. Software engineering can be a mentally draining task, and just like with physically draining tasks your body needs time to recover its strength. Nobody would expect an athlete to last very long doing back to back events without recovery time between them - they'd end up injured. Your brain is similar.
Recognizing that and accommodating it is a sign of maturity for both an engineer and a manager.
> What kind of runner can run as fast as they possibly can from the very start of a
race?
> [Audience reply: Sprinter]
> Right, only somebody who runs really short races, okay?
> [Audience laughter]
> But of course, we are programmers, and we are smarter than runners, apparently, because we know how to fix that problem, right? We just fire the starting pistol every hundred yards and call it a new sprint.
Recognizing that and accommodating it is a sign of maturity for both an engineer and a manager.