[chipsy]

Echoing the mentions of cognitive load, I get the impression that only about an hour or two of "forceful mental effort" - the period when you're hovering outside of a flow state and have to reassemble the problem you're working on - actually takes place during work hours.

This would account for why it becomes incredibly difficult to polish up creative work after a certain point(fit+finish of software, detailing artwork, tone and timbre in music); once you've solved all the big problems. You're spending all your time on figurative hands-and-knees, straining to find the little things - even though you may know how to attack a problem once you're aware of it, collecting the necessary data to turn the process into a fast feedback loop is hard. Hence why polish work is absolutely exhausting, because you're constantly knocked out of flow.