"More hours, more done"

The central belief behind long hours is so obvious that it hardly seems like a belief. If you work fifty-five hours, you get more done than if you work forty. Every extra hour adds something, even if the late hours aren't your best.

The best evidence I know on this comes from a surprising place. During the First World War, Britain was desperately short of shells. Munitions factories ran very long hours, often seventy a week and more, with Sunday working brought back in. The government became worried that the hours were damaging both the workers and the output, and set up a committee to investigate. Its researchers collected careful records, week by week, of how many hours groups of workers put in and how much they produced.

A century later the Stanford economist John Pencavel went back to those records and analysed them with modern methods. What he found was this. Up to about forty-nine hours a week, output rose in step with hours, so that more time gave proportionally more shells. Beyond forty-nine hours, each extra hour added less than the one before. Output reached its maximum at around sixty-three hours a week, and after that it fell. A seventy-hour week produced barely more than a fifty-six-hour week. Those fourteen extra hours at the machines yielded almost nothing.

I find this study persuasive for a reason beyond the numbers. Nobody could say that these workers, most of them women, lacked commitment. They were making shells for husbands and brothers at the front, in a war the country believed it might lose. If motivation could overcome fatigue, it would have done so there, and it didn't.

You might object that you don't make shells. Your work is mental, and you can do it sitting down. That's fair, and I can't point to an equally clean study of planning managers. There's some modern evidence, though. Marion Collewet and Jan Sauermann studied call centre agents in the Netherlands, whose hours varied from day to day because of central scheduling. As an agent's hours went up, their average time to handle a call went up too. They became less productive as the day went on, and most of them were part-timers who weren't working anything like seventy hours.

My own view, which is interpretation, is that mental work is likely to suffer more from long hours than machine-minding does. A tired machinist makes shells more slowly. A tired planner makes decisions worse, misses things, writes emails that need a second email to correct, and spends forty minutes on a paragraph that would take ten in the morning. Slow work at least stands. Bad work has to be found and fixed, and it's usually fixed during someone's good hours the next day.

Go back to the two hours between five and ten to seven. You reworded a report that was already fine, conducted an email exchange that generated itself, and tidied a private spreadsheet. If Pencavel's curve applies to you at all, that's what the flat part of it looks like from the inside. You feel as though you're working because you're at the desk and you're tired. But very little got done.

So the late hours add less than they seem to. The next chapter argues that they also take something away from the hours before them.