Non-stop activity isn't the apotheosis of productivity. It is its adversary. Researchers are learning that it doesn't just mean that the work we produce at the end of a 14-hour day is of worse quality than when we're fresh. This pattern of working also undermines our creativity and our cognition. Over time, it can make us feel physically sick - and even, ironically, as if we have no purpose. The idea that you can indefinitely stretch out your deep focus and productivity time to these arbitrary limits is really wrong," says research scientist Andrew Smart. "If you're constantly putting yourself into this cognitive debt, where your physiology is saying 'I need a break' but you keep pushing yourself, you get this low-level stress response that's chronic - and, over time, extraordinarily dangerous." One meta-analysis found that long working hours increased the risk of coronary heart disease by 40% - almost as much as smoking (50%). Another found that people who worked long hours had a significantly higher risk of stroke, while people who worked more than 11 hours a day were almost 2.5 times more likely to have a major depressive episode than those who worked seven to eight. The reason we have eight-hour work days at all was because companies found that cutting employees' hours had the reverse effect they expected: it upped their productivity. If eight-hour days are better than 10-hour ones, could even shorter working hours be even better? Perhaps.