[UglyToad]

It's interesting to hear that this is not just peculiar to software. I have no real understanding of what other jobs involve but I can well believe there's a similar experience in other mentally (and physically!) demanding jobs.

Flow is one of those things that I think is related to interest in the task at hand but is also, as you point out, difficult to recover once disturbed. It's also highly unpredictable. The 2-3 hours I spend productively might not be in a continuous block but also the time spent giving the appearance of productivity makes it harder to (re)enter flow. If work was structured such that you could work when productive and take care of life admin when not, rather than a discrete chunk of time every day, I feel like it would significantly improve mentally demanding labour.

Ultimately I'd like to see everyone work less [0] for which I think the driving force has to be regulation (companies demanding these hours are just more-or-less rational actors in the system), the productivity gains are there but we seem to be busier than ever - we've thereby created new fields of work (TaskRabbit, Deliveroo, etc) for people to work in, but at little benefit to people or society.

[0]: http://www.zpub.com/notes/idle.html