" But I am just raising the point that you can always push further if you want to."

I have had the opportunity to work on difficult stuff for a few years and after around 35 hours per week I was pretty much shot. I still thought about it in my free time but there definitely was no point sitting in front of the screen because I wouldn't get anything done.

I'll admit there are some high performance workers (you could call them athletes) who can spend 80hrs/week working and producing but these are rare from my experience. Most people I have seen that work 80 hr weeks have a lot of downtime in between. The only difference is they spend that time in the office.

I've never met someone who could do 80 hours of focused work. Everyone I've seen who puts in a lot of hours doesn't achieve more results than if they had put in 40 hours of focused work. They feel like they're making progress, but they make many mistakes along the way and then later have to spend crazy hours making up for those mistakes, making more mistakes, etc... ad nauseum.

You can put all your energy into paddling a canoe, but if it's still tied to the dock you're going nowhere.

The whole reason I am bringing this up is because I have done 70+ hours of focused work on many occasions.

It's a more-than-linear improvement over 40 hours, because when pro-rated you have a lower density of context switches, getting-back-up-to-speed, etc, as happen in the morning or when you eat or such.

Maybe too many people have done long-term damage to their attention spans via the internet? I dunno.

At the risk of being mildly provocative ... are any of the people you know, who can't do more than 40 hours of work in a week, world-class in their field? If not, maybe there is a causal link between these two things?

I've done weeks like that myself, for a few weeks at a time. My comment was addressed at people who do 80 hours routinely. I've never met someone world class who was doing that. I have met some world class people, but they kept to a reasonable schedule.

I'm sure these 80 hour continuous productivity guru's exist. I'm just saying they are so exceedingly rare to effectively be unicorns.

Supposedly Bill Gates was like this when he was young. But I would compare these people to elite athletes. Most people can train as much as they want but will never reach that level. they may risk injury on the way though.

I have done 80 hours week productively from time to time but never for long. In startup I worked at we worked nights and weekends but a lot of it ended up being playing foosball and pool.