Regarding "being both mentally and physically fit", while I agree that it's not intelligence on its own, I think this is a good description of the biggest sourc

Regarding "being both mentally and physically fit", while I agree that it's not intelligence on its own, I think this is a good description of the biggest source of variance in the intelligence I can apply to a task at any given time. I'm way smarter when I'm well-rested, well-fed, being active, etc.