Brooks jokingly says she “hates” Sandberg, but of course, both writers have good intentions: Sandberg wants more working moms to be leaders, or at least professionally ambitious. Brooks wants more working moms to be in possession of their marbles.

There is evidence that trying to over-achieve on both the parenting and working fronts simultaneously can be maddening. Multiple studies have found steep declines in the well-being of women over the decades relative to men. Working moms multitask more—and are less happy about it. American working hours are crazy: Each year we work a month more on average than we did in 1976, and 62 percent of high-earning professionals work 50 hours a week or more. Grade-school kids sleep nine or 10 hours a night. Even if their schedules coordinate perfectly, kids of executives might have, at most, a couple hours with their parents each weekday.

U.S. policy doesn't exactly make it easy to lean out even temporarily. Only about a fifth of moms get fully paid maternity time off, and high-powered “key employees” can be legally denied reinstatement if they go on family or medical leave.

Pew Research Center

Parents who truly wish to split the “workday” between actual work and childcare might also discover that the U.S. lacks a culture of part-time work, even though more than half of American working moms would prefer to work part-time or not at all. Part-time employees at American companies are much less likely to have access to benefits like retirement, medical care, and sick leave than are their full-time colleagues. U.S. workers are some of the least likely among the OECD nations to work part-time. (And even in countries where working less is accepted, the career disparity persists because it’s generally women, not men, who choose this route.)

While working less may pay mental-health dividends, it’s doubtful you’d get to be COO of Facebook by turning down an extra project in order to have more time to read novels (or read them to your kids). In clinical studies, American participants viewed women who worked on a flexible schedule as having “less job-career dedication and less advancement motivation.” And even for exempt employees, working more is directly associated with earning more within the same job. Women who cut back on work in order to accommodate their families may end up sacrificing career opportunities to their colleagues who don’t facing the same dueling responsibilities, whether they are men with supportive wives or women without children.

To compensate, Sandberg argues that men should do more housework and childcare in order to free up their wives to spend more time getting ahead at work. But that, too, is bound to leave out women who don’t have especially enlightened husbands, or those whose partners lack flexible work hours, or, you know, single moms. And only 15 percent of companies offer paid leave for new fathers, so many dads don’t have the option.

Brooks says what's key is that we must all lean back en masse, in solidarity, as though performing an edgy modern dance together:

“When women—or men—lean out alone, they end up getting eased out, or just dropping out in despair,” she writes.

In a way, though, this is the ultimate prisoner’s dilemma. With American work culture the way it is, even if the vast majority of us lean out in revolt, the promotion, raise, or “Room Mom” award will go to those (wo)men still leaning in.