How many employed American mothers work more than 50 hours a week? Go on, guess. I’ve been asking lots of people that question lately. Most guess around 50 percent.

The truth is 9 percent.

Nine percent of working moms clock more than 50 hours a week during the key years of career advancement: ages 25 to 44. If we limit the sample to mothers with at least a college degree, the number rises only slightly, to 13.9 percent. (These statistics came from special tabulations of data from the US Census Bureau’s 2011 American Community Survey.)

This “long hours problem,” analyzed so insightfully by Robin Ely and Irene Padavic, is a key reason why the percentage of women in top jobs has stalled at about 14 percent, a number that has barely budged in the past decade. We can’t expect progress when the fast track that leads to top jobs requires a time commitment that excludes most mothers — and by extension, most women. A recent study by Joni Hersch of Vanderbilt Law School found that the mothers most likely to enter the fast track — graduates of elite universities — are less likely to be working full time than mothers with less prestigious degrees. Only 45.3 percent of mothers who graduated from top-tier institutions — and only 34.8 percent of MBAs — have full-time jobs. Most aren’t full-time homemakers: in addition to parenting, they typically have part-time jobs or community service roles. But you can bet your boots it’s under-valued work that rarely, if ever, leads to positions of power.

Despite the obvious importance of the hours problem, progress has been limited. An increasingly common response is to declare victory.

“What flexibility means today is not part time,” the head of work-life at one large organization told me recently. “What people want is the ability to work anytime, anywhere.” That’s true if your target labor pool is twenty-somethings and men married to homemakers. The head of HR at another large organization asked, when I described the hours problem, “What do you mean, how can we get women to work more hours?”

We can’t get mothers to work more hours. We’ve tried, and failed, for forty years. Mothers won’t bite for a simple reason: if they work 55 hours a week, they will leave home at, say, 8:30 and return at 8:30 every day of the workweek, assuming an average commute time. Most moms have this one little hang-up: they want to see their children awake. Increasingly, many fathers do, too.

And yet, after forty years of intensive effort, the work-life frontier looks grim. Recent events confirm this. In late 2012, Bank of America announced that it was preparing to add more restrictions to its work-from-home program, reportedly to increase efficiency. Early this year, Best Buy CEO Hubert Joly ended the company’s “results only work environment” (ROWE) program that judged corporate employees only on (gasp!) performance, and not where or how long they worked. And, of course, Marissa Mayer eliminated telecommuting at Yahoo! (Why have we only heard about that one? Because women CEOs are held to higher standards, that’s why.)

Why are workplace flexibility programs so hard to sustain? The business case for such programs’ benefits is well known. The elimination of ROWE is particularly striking because the path-breaking work of Erin Kelly, Phyllis Moen, and their colleagues, has produced rigorous regressions that ROWE reduced turnover and turnover intentions, reduced employees’ interruptions at work, reduced time employees’ engaged in work of little value to the company, and increased employee’s sense of job involvement, using rigorous social science methodology.

But the issue here is not money. At issue are manliness and morality.

For upper-middle class men, notes sociologist Michèle Lamont, ambition and a strong work ethic are “doubly sacred. . . as signals of both moral and socioeconomic purity.” Elite men’s jobs revolve around the work devotion schema, which communicates that high-level professionals should “demonstrate commitment by making work the central focus of their lives” and “manifest singular ‘devotion to work,’ unencumbered with family responsibilities,” to quote sociologist Mary Blair-Loy. This ideal has roots in the 17th century Protestant work ethic, in which work was viewed as a “calling” to serve God and society. The religious connection has vanished….or has it?

Blair-Loy draws parallels between the words bankers used to describe their work — “complete euphoria” or “being totally consumed” — and Emile Durkheim’s classic account of a religion ceremony among Australian natives. “I worshipped my mentor,” said one woman. Work becomes a totalizing experience. “Holidays are a nuisance because you have to stop working,” said one banker interviewed by Blair-Loy. “I remember being really annoyed when it was Thanksgiving. Damn, why did I have to stop working to go eat turkey? I missed my favorite uncle’s funeral, because I had a deposition scheduled that was too important.”

Work devotion marries moral purity with elite status. Way back when I was a visiting professor at Harvard Law School, I used to call it the cult of busy smartness. How do the elite signal to each other how important they are? “I am slammed” is a socially acceptable way of saying “I am important.” Fifty years ago, Americans signaled class by displaying their leisure: think banker’s hours (9 to 3). Today, the elite — journalist Chrystia Freeland calls them “the working rich” — display their extreme schedules.

Not only is work devotion a “class act” — a way of enacting class status — it’s also a certain way of being a “real” man. Working long hours is seen as a “heroic activity,” noted Cynthia Fuchs Epstein and her co-authors in their 1999 study of lawyers. Marianne Cooper’s study of engineers in Silicon Valley closely observes how working long hours turns pencil pushing or computer keyboarding into a manly test of physical endurance. “There’s a kind of machismo culture that you don’t sleep,” one father told her. “Successful enactment of this masculinity,” Cooper concludes, “involves displaying one’s exhaustion, physically and verbally, in order to convey the depth of one’s commitment, stamina, and virility.”

Workplace norms cement felt truths that link long hours with manliness, moral stature, and elite status. If work-family advocates think they can dislodge these “truths” with documentation of business benefits, they are sorely mistaken. The coverage of Marissa Mayer’s decision to eliminate telecommuting highlights how even hard data get lost in the shuffle.

The press coverage acknowledged the robust evidence that telecommuting boosts productivity — and then dismissed it as if productivity were a silly little side-issue. “Okay, okay, it might boost productivity,” was the argument, “but it inhibits innovation.” Okay, but after you spark those great ideas in the lunchroom, you need quiet time to work them through–for which telecommuting is perfect. No mention of that, though.

So here’s where we stand. If institutions are serious about advancing women, they’ll have to address the hours problem — that’s the only way to get a critical mass of women poised for leadership. But we’ll never address the hours problem until we open up a conversation about what drives it.

It’s not productivity. It’s not innovation. It’s identity. If you’ve lived a life where holidays are a nuisance, where you’ve missed your favorite uncle’s funeral and your children’s childhoods, in a culture that conflates manly heroism with long hours, it’s going to take more than a few regressions to convince you it wasn’t really necessary, after all, for your work to devour you.