[TeMPOraL]

I strongly agree. I found for myself that when I have a clear goal and a path toward it already figured out, I can just sit down and code like crazy for long hours[0], even if I'm tired or start sleeping less. But if I need to do conceptual work (or just didn't think enough about the problem), trying to do anything when not being well-rested (7+h of sleep) is a waste of time.

[0] - as long as it's not Work. I'm a sad case of extreme intrinsic vs. extrinsic motivation issues; my best well-rested extrisincly motivated hours are about 25% as productive as sleep-deprived intrisinc-motivated ones. I have no clue how to fix this.