> there is no limit where one can say, "My work is done"
I'm a couple years into my first software job, at Google. We don't do performance evaluations relative to whether you're doing as much work as you're capable of in 40 hours. You're evaluated against a fixed rubric corresponding to the job level. In other words, if you're capable of doing a Software Engineer N's worth of work in 40 hours and your title is Software Engineer N-1, you can either put in the 40 hours and get promoted to Software Engineer N eventually, or you can work less and still be perfectly productive relative to your current role's expectations. Plenty of people make that latter choice and work well under 40 hours.