[Smudge]

I'd be shocked if those 12-16 hours you apparently put in for "weeks on end" are truly your most productive. They may certainly feel "mentally strenuous," but that doesn't mean your cognitive limit isn't decreasing as the days and weeks go on.

I find that I can focus intensely for shorter bursts over a couple hours, but then I hit my limit and need to push the really hard stuff aside for a while. Sure, I can crank through a ton of tedious or menial tasks (and there are certainly plenty of them), but that's really not the same.

When I complain about being expected to sit around for 8, 9, 10 hours a day (and I do occasionally complain), it's not because I'm rationalizing lazy habits or want to get out of work. I love my work.

No -- It's because in only 3-4 of those hours I will finish 90% of what I ultimately get done in a day. The trick is in knowing how to optimize those hours of productivity, and when to go home and give your brain time to decompress.