Earlier quoted context omitted.
I would say that learning draws from the pool of "mental energy", but working out draws from the pool of "physical energy". Just because your brain is tired, it doesn't mean that your biceps are.
Yeah exactly. After a hard day when my brain is frazzled, a workout will actually make me feel better.
Being mentally worn out just kinda makes you feel like shit. It's a terrible state to be in, you don't want to do anything, but doing nothing also feels bad.