Some of the most successful people in the world have advice for the rest of us: chill out a little bit.

Mexican billionaire Carlos Slim -- the second-richest man in the world -- told the Financial Times last week that the typical work life of five-day, 40-hour weeks with a goal of retiring in your 60s doesn't work. Instead, he said, people should work 11-hour shifts, three days a week, and plan to work well into their 70s.

Two weeks ago, Google CEO Larry Page told a conference that "the idea that everyone needs to work frantically to meet people's needs is just not true." Most people, he said, could support themselves with less money and be happier with more time off. He said we need a coordinated way to adjust the workweek, perhaps with two part-time workers replacing one full-time worker. "Most people like working, but they'd also like to have more time with their family or to pursue their own interests," he said.

What are these guys thinking?

There are two issues here.

One is that the concept of retirement is a recent experiment, and it hasn't gone very well.

Before 1940, more than half of men over age 65 were still active in the workforce. In 1900, more than three-quarters of elderly men were still working. Most people just worked until they died.

It's just the last 50 years that we've thought most people have a right to stop working in their 60s and relax. And we haven't prepared well for it. Social Security can cover the basics, but according to Nielsen Claritas, Americans age 55 to 64 have a median net worth of $180,000 -- less than they'll likely need for health-care spending alone during retirement.

A lot of retirees aren't even that happy with their freedom. According to a study by the Skipton Building Society, any added happiness that comes from retiring wears off after just 10 months. Retirees had a laundry list of complaints, from "I miss the camaraderie I had at work," to "I didn't have many hobbies or interests to fill my time," to "I put on weight as I wasn't as active."

Working part time into your 70s, as Slim suggested, would take care of both problems. It would add more income to help avert the retirement shortfall you hear so much about. And since, in Slim's world, workers would have enjoyed four-day weekends for their entire careers, working in retirement wouldn't cut into the amount of free time you get over your lifetime. You would actually have more free time when you're young, able-bodied, have kids, and can travel. Some jobs wouldn't allow working into your 70s, of course. But most could. According to the Center for Economic and Policy Research, two-thirds of 58-year-olds are in nonphysically demanding jobs.

The second issue is maximizing productivity while you're working.

Monday through Friday nine-to-five is probably the most invasive work schedule you can create. It leaves no personal time in the morning, very little in the evening, and barely enough to run errands on the weekend.

When your work schedule leaves no time for your personal life, you have to mix the two, constantly switching your mind from work life to personal life throughout the day. And that's the worst possible way to get stuff done.

In her book Overwhelmed, Brigid Schulte writes that, compared with past generations, workers today feel stretched for time. But it's not because we're doing more. It's because we're trying to do too many things at the same time, rather than in separate, focused chunks. "It's role overload," she writes. "It's the constant switching from one role to the next that creates that feeling of time pressure."

Letting people work hours that fit their personal lives can massively improve productivity when they're on the job. Ricardo Semler, CEO of Brazilian conglomerate Semco, writes in his book The Seven-Day Weekend:

If I demand that a worker show up at 8:00 A.M., even if she is someone who regularly sleeps until 9:00, all I will get is a couple of hours of her least productive time. And if I'm closed down at 6:00 P.M., I'm sending her home just as she's hitting her stride. Her biorhythms may dictate that her best hours are from six to eight. Someone else may be alert and prolific after a twenty-minute catnap in the afternoon. If I insist on standard work hours, I may be sacrificing a certain amount of employee potential every day. By encouraging uniformity, I lose productivity. By changing the rules, we remove the obstacles that throw people's lives out of whack. When we tell people they're free to work closer to their homes, to come to the office only when they need to, to work odd hours, or to take a weekday off in exchange for work on a Sunday, we're really telling them that there are no rules when it comes to finding a balance in their lives.

Working into your 70s is possible, and will probably have to occur. Working flexible hours is possible, and more companies are moving in that direction.

But there's something we shouldn't expect to happen: people working fewer hours overall and spending more time in leisure.

Economists have been predicting for decades that people would work fewer hours as the country got richer. John Maynard Keynes predicted that by 2030 we'd all be working only a few hours a week. In 1960, Richard Nixon predicted that by 1990 the average workweek would be just 22 hours.

Nothing like this happened. Adjusted for inflation, the median household earns more than three times as much today as it did 80 years ago. But we still work about as many hours.

People's expectations of what a good life entails grow just as fast as their earnings. That will always be the case, and no matter how rich the country gets, most people will work as much as they can while staying sane. That's probably about 40 hours a week. So while everyone could work less, I doubt many of us ever will.

Check back every Tuesday and Friday for Morgan Housel's columns on finance and economics.