For over 150 years, many of history's great economists, from Karl Marx to John Maynard Keynes, predicted that machines would usher mankind into a scholarly fantasy of enlightened leisure. Robots would, they argued, serve all of our needs while we spent the days reading classics, debating philosophy, and indulging in fine art.

Well, it turns out that the prophecy was half right. Many prime age workers enjoy unprecedented levels of leisure, but—and here’s the other half—they would apparently rather doze off into a midday nap watching the Desperate Housewives of New Jersey than debate the merits of Plato's Republic.

The U.S. government's annual survey of how Americans spend their day, the American Time Use Survey, continues to show that disaffected workers fill their extra free time sleeping and watching TV. Time spent on education, taking care of others, or self-improvement has not fully filled their free hours.

For decades, robots have slowly been replacing human work. For a time, the elimination of one type of work simply meant it was filled with another. For instance, as appliances automated the drudgery of homemaking, housewives threw in their aprons and increased their hours in the workforce—granting them more social and economic power. But we are getting to a point where less mundane work is needed, which is why the work week, on average, is shrinking for some.