Carlos Slim, the Mexican telecommunications magnate, has proposed that workers all transition to three-day workweeks and distribute their careers over a much larger number of years. As quoted in the Financial Times:

“With three work days a week, we would have more time to relax; for quality of life. Having four days [off] would be very important to generate new entertainment activities and other ways of being occupied.”

The 74-year-old self-made magnate believes that such a move would generate a healthier and more productive labour force, while tackling financial challenges linked to longevity.

This is actually not such a revolutionary idea. Economists and futurists have been thinking about shrinking the workweek for a long time. The most famous predictions, though, were predicated on the idea that the workweek would contract because productivity gains would dramatically reduce the need for human labor. It’s the more optimistic version of the “robots are stealing our jobs” narrative.

As John Maynard Keynes argued back in 1930, once wages were high enough that people could make enough money in a few hours to meet their basic human needs, they would stop working so much. Workers might end up in jobs lasting “three-hour shifts or a fifteen-hour week,” he wrote.

He even goes on to imagine the agony later generations would endure as they struggled to fill their abundant free time. “To those who sweat for their daily bread leisure is a longed-for sweet — until they get it,” he writes. Later he says:

[T]here is no country and no people, I think, who can look forward to the age of leisure and of abundance without a dread. For we have been trained too long to strive and not to enjoy. It is a fearful problem for the ordinary person, with no special talents, to occupy himself, especially if he no longer has roots in the soil or in custom or in the beloved conventions of a traditional society. To judge from the behaviour and the achievements of the wealthy classes to-day in any quarter of the world, the outlook is very depressing! For these are, so to speak, our advance guard-those who are spying out the promised land for the rest of us and pitching their camp there. For they have most of them failed disastrously, so it seems to me–those who have an independent income but no associations or duties or ties–to solve the problem which has been set them.

This futuristic short workweek also took hold in pop culture a few decades later. You may recall that George Jetson — created in 1962, but imagined to be living in the year 2062 – grumbled about his two- or three-hour workdays. His wife compared such grueling hours to sweatshop work.

The number of working hours has indeed contracted over time, though not close to George Jetson levels. And the decline is probably at least partly driven by the changing composition of the workforce (i.e., more women, who are more likely to work part-time).

Source: Organization for Economic Cooperation and Development

So why did Keynes’s predictions prove so wrong? There are many possible explanations. For one, the vast improvements in living standards Keynes foresaw have not been equally distributed. Many people also derive pleasure from working. And Keynes didn’t anticipate all the cool, highly coveted things (and services) that would be invented in the decades after his passing that would keep people wanting to earn income beyond that which enabled them to meet their basic needs.

Lots of jobs are also not easily divisible, meaning it’s hard to break them into three-day-a-week increments even if workers did find that three days of labor provided sufficient income to meet all their needs and wants. Which is probably the strongest argument against Slim’s somewhat utopian, work-sharing vision. It would be great, though, if we could find more ways to make jobs divisible and shareable, since that would probably draw more people (especially parents and others with substantial family responsibilities that don’t allow them to work full-time) into the labor force.

Catherine Rampell is an opinion columnist at The Washington Post.