> Brain work for me is like muscles for others - if I don’t squeeze out every ounce of energy from my brain with problems all day, I feel like I haven’t lived a full day. Many people prefer good workouts instead, if they don’t their body is punitive with restlessness and sleeplessness.

I need both.

Too little brain work and my thoughts are racing (unproductively) and my sleep needs fall down to ~4h (happens on vacation) which isn’t actually enough to make me feel rested.

Too little physical activity and I’m restless and can’t focus, can’t sleep, and generally stuff falls apart.