According to Charles Czeisler, the chief of the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital, over the past five decades our average sleep duration on work nights has decreased by an hour and a half, down from eight and a half to just under seven. Thirty-one per cent of us sleep fewer than six hours a night, and sixty-nine per cent report insufficient sleep. When Lisa Matricciani, a sleep researcher at the University of South Australia, looked at available sleep data for children from 1905 to 2008, she found that they'd lost nearly a minute of sleep a year. It's not just a trend for the adult world. We are, as a population, sleeping less now than we ever have …

When we try to boost productivity by expanding our waking hours, we aren't doing anyone any favors. Studies have shown that we are less productive, less insightful, less happy, more likely to get sick. We systematically undervalue sleep, and yet it is fundamental to our present and future performance.