To understand why female lawyers, doctors, bankers, academics, high-tech executives and other, often expensively pedigreed, professionals quit work to stay home, you need not search their souls for ambivalence or nostalgia. In fact, searching their souls guarantees that you won’t get the story, because it’s not to be found in individual decisions and personal stories, which are always complicated and hard to parse, but in the structural realities of the American workplace. And by this I don’t just mean the family-unfriendly policies of the kind Marissa Mayer is accused of advancing—though refusing to let workers telecommute doesn’t help, and let’s not even talk about how few American companies have on-site child care or adequate parental leave. I mean that among the professional and managerial classes, success at work requires more hours in the office, more hours on the computer at home, more trips out of town, and a much less predictable schedule than it did in Betty Friedan’s day. The life of a Joan or a Peggy at an advertising agency looks almost easy by comparison.

To reject a high-flying career is not to reject aspiration; it is to reject a kind of madness.

When Friedan was writing The Feminine Mystique, the 40-hour-a-week office job was still a norm, even for executives—a norm well on its way to changing, but a norm nonetheless. Today, whether you’re male or female, if you’re taking home an upper-middle-class salary you’re expected to work an average of 50 hours, and probably more, a lot of it after you’ve gone home. As of 1997, the average workweek for a man with graduate education was 50 hours, and for a women 47—that three-hour difference can be accounted for, of course, by all the women who went on mommy tracks. Among American dual-career couples, in the 1990s, 15.2 percent of those with at least college degrees worked a joint 100 hours a week or more, whereas only 9.6 of couples without diplomas did that. Try to imagine what that 100-hour workweek looked like to a child: that’s five 10-hour days, plus commutes, for both parents. And those are just averages—for people at the top of their fields, the numbers were a great deal bigger.

That the workweek is ballooning for America’s educated, salaried classes, even as it’s shrinking for less educated, hourly workers, or turning into part-time work, has been called the “time divide”—the increasing inequality of time spent working, which tracks with the rise of economic inequality. As of 2002, for example, Americans in the top fourth of earners toiled an average of 15 hours more than earners in the bottom fourth. I called the sociologist Jerry Jacobs, who along with another sociologist, Kathleen Gerson, coined the phrase in their 2005 book The Time Divide, to ask what the time divide looks like after the recession, now that so many workers, including white-collar ones, are unemployed. The workforce is more unequal than ever, he told me. “People who get a job feel that they have to be willing to work whatever they’re asked to work,” he said. And those lucky enough to work are working with greater intensity. “The American economy is producing more than it did before the recession,” he continued, “and it’s doing it with 8, 10, 12 million fewer workers. Employment isn’t where it was pre-recession, but the productivity, the total volume of stuff being produced, is higher. The only way that can happen is if people are working longer and harder.”

Confirming the sense that those at the top of the heap are feeling the pinch of our increasingly competitive world are studies reporting that they’re more stressed out than they used to be. They juggle more tasks more quickly and with more interruptions, do more work after hours at home to get it all done, and take more out-of-town trips. In 1977, according to a survey by the go-to organization for work-family balance, the Work and Families Institute, 65% of men said they had to work very hard at their job, and 52% said they had to work very fast. By 2008, those figures were 88% (very hard) and 73% (very fast). In another study, the institute reported that half as many high-paid managers and professionals (24%) as low-paid employees in other occupations (48%) say they’re able to wall off their non-work hours from contact from co-workers, supervisors, or clients. As for business travel, among employees whose earnings put them in the bottom quarter of the American pay scale, only 9 percent said they had to do it, whereas among those in the top quarter, 38 percent said they had to travel.

If such sacrifices of time are now routine for office workers, what does it take to move up through the ranks? Jacobs, who teaches at the Wharton School of Business at the University of Pennsylvania, told me the story of a recent graduate who had been determined to be among the top ten performers among several hundred peers at a Wall Street firm. He worked non-stop for two years, getting four to five hours of sleep a night. By the end of that period, he was named the very top performer in his group—at which point he decided he’d had enough, and left finance.