Working eleven or more hours a day had at least doubled the risk of depression. Those working fifty-five hours a week or more began, in midlife, to suffer cognitive loss. Their performance was poorer when tested for vocabulary, reasoning, information processing, problem solving, creativity, and reaction times. Such mild cognitive impairment also predicted earlier dementia and death.
It is common for a person experiencing fatigue to be more rigid in thinking, have greater difficulty responding to changing or abnormal circumstances, and take longer to reason correctly. Tired and overwhelmed, we want problems to go away—we don’t care how—because we lack the capacity to analyze or solve them.
Working through the night is heroic; long hours are interpreted as commitment. When companies fail or big deals don’t deliver (mergers and acquisitions have a failure rate of 40 to 80 percent), nobody stops to consider that exhausted brains might be the culprits.
Productivity isn’t linear. We can work well for forty hours a week but no more than that. After forty hours we get tired and make mistakes—so we need extra time to clear up the mess we’ve made.