Even something as natural as sleep is subject to social pressure, and figuring out why we sleep badly is more difficult than it seems. Is sharing beds with a significant other stopping us from falling into deep sleep? Did industrial capitalism destroy a healthier pattern of shorter, more frequent sleep time in favor of a single eight-hour block? Or is it the tyranny of the clock itself, pulling people out of "personal time zones" for a single standardized time? At The New Yorker, Elizabeth Kolbert takes a look at the spate of recent books on sleep and sleeplessness, trying to answer a simple question: why are we all so tired?