You'd expect Silicon Valley working practices to be less optimal than those in mature industries, because, well, the industries aren't mature. The companies are often run by people with minimal management experience, and the companies themselves are too short-lived to develop the kind of institutional memory that would be able to determine whether such policies were good or bad. Heck, most of SV still follows interview practices that have been actively shown to be useless, to the extent that they've been abandoned by the company that originated them (Microsoft). Success is too random for these things to be noticeable; the truth is that in SV, being 50% less efficient probably has negligible effects on your odds of success, because the success or failure of a given company is massively overdetermined (in one direction or the other) by other factors.
The only people in a position to figure this kind of thing out, and then act on that knowledge, are the venture capitalists - and they're a long way removed from the action (and anyone smart has already left the business since it's not a good way of making money). Eventually I'd expect VCs to start insisting that companies adopt 40-hour policies, but it's going to take a long time for the signal to emerge from the noise.
You'd expect Silicon Valley working practices to be less optimal than those in mature industries, because, well, the industries aren't mature.
On the one hand, yes. On the other hand I expect the working practices of mature industries to have been formed during the times of typewriters and three-ring binders.
Conventional wisdom, and many studies, hold that 40 hours of work per week are the optimum before exhaustion starts dragging your productivity down too much to be worth it. I read elsewhere that the optimum is even lower for creative work, namely 35 hours per week, though the sources I found don't all seem to agree.
In contrast, many tech companies in silicon valley demand (or 'encourage', which is the same thing in practice) much higher work times. 70 or 80 hours per week are sometimes treated as normal.
How can this be?
Are these companies simply wrong and are actually hurting themselves by overextending their human resources? Or does the 40-hour week have exceptions?
How high is the variance in how much time people can work? If only outliers are hired by such companies, that would explain the discrepancy. Another possibility is that this 40 hour limit simply does not apply if you are really into your work and 'in the flow'. However, as far as I understand it, the problem is a question of concentration, not motivation, so that doesn't make sense.
There are many articles on the internet arguing for both sides, but I find it hard to find ones that actually address these questions instead of just parroting the same generalized responses every time: Proponents of the 40 hour week cite studies that do not consider special cases, only averages (at least as far as I could find). Proponents of the 80 hour week claim that low work weeks are only for wage slaves without motivation, which reeks of bias and completely ignores that one's own subjective estimate of one's performance is not necessarily representative of one's actual performance.
Do you know of any studies that address these issues?