[jokethrowaway]

That's not necessarily true.

Maybe people can't produce more than 4 days of work per week or 5 hours per day; in that case the productivity would be the same and people working more are essentially wasting time.

My empirical evidence say otherwise (sample_size=1) I can be quite productive up to ~70hrs doing knowledge work (I've been on it for 8 months, hours are tracked and connected to tasks, no idling is counted), but that's pushing it and it might not be sustainable for longer period of time. My will to live is certainly at historical lows.

Lawyers in big law can also do 60-80 hours (while ruining their life) so I think it's reasonable.

I've heard people in other professions (eg. nurses) pushing 90-100hrs but they are not actively thinking all their working time.