Liliana Vess Defiant Necromancer

One day, Ignis, that would be you, too.

"Mostly correct, my darling," Liliana told him. "But first, physical exercise is mentally taxing, and physical exhaustion moreso. Intense physical training and intense cognitive tasks affect the same region of the brain. So when you do intense physical exercise, you are actually worse at cognition, my darling, and need to rest your brain and body both."

She went to steal another raspberry. This was called sharing, Ignis. Enforced sharing.

"Your brain is a muscle much like any other. It gets fatigued when you work it and it needs to rest. Ignoring that and pushing it to continue simply further degrades its learning capabilities, at least until you let it rest. So frivolous and light mental activities serve a valuable purpose: they allow for your brain to rest, while still providing mental stimulation. This may frustrate you deeply, my darling, but the fact of the matter is, rest and relaxation, both mental and physical, are actually required for optimal performance."