In Sheryl Sandberg’s much-discussed new book about moving more women into leadership roles, it’s disappointing that she writes nothing about a Facebook tradition called “lockdown.”

Facebook, where Sandberg famously works as chief operating officer, has gone into lockdown mode when facing competitive threats or in the run-up to new-feature launches. Co-founder and CEO Mark Zuckerberg gives the signal by flipping on a pink neon sign.

As described in Fortune, in a lockdown Facebook’s workweek literally goes to 24/7. Kids are brought to the company for dinner and a hug before bedtime, and then the parents trudge back to their cubicles.

In “Lean In: Women, Work, and the Will to Lead,” Sandberg writes about the effects of sexism and what women need to do to jump over those hurdles into leadership. Yet she doesn’t have much useful to say about scaling back overwhelming time demands — each person’s version of lockdown — that make also enjoying a family life so challenging. And that’s the highest hurdle of all.

Sandberg’s “Lean In” is well worth sticking in the bag for spring break, important if only for how it has fueled lively conversations about why women aren’t better represented in leadership jobs.

It’s aggravating to see that just 4 percent of the CEOs in the Fortune 500 are women, and suggestions that “you can’t have it all” because life is inherently full of constraints and trade-offs are beyond aggravating. “Having it all” only means both a professional life and a family life: Why must that be beyond reach for so many people?

Sandberg’s take is that women “lean back” too much in their careers, partly responding to subtly different workplace rules. Many women, for instance, figure out that when they commandeer a meeting they get sniped at for being bossy, while men who do so are praised for showing leadership. Go ahead, Sandberg writes, lean in.

As for managing a family alongside a demanding job, there’s too much leaning back here, too. She finds it exasperating to watch high-potential women holding back from chasing top jobs because they are thinking about having children.

She writes about hearing a McKinsey & Co. boss explain to his staff that the only reason people gave when quitting was burnout from time and travel demands, but he couldn’t help but notice that in each case the person had unused vacation time. The lesson she gets out of this is to at least try managing a demanding job on your own terms.

McKinsey, the global consultancy, employs some of the best business thinkers, but it’s striking how impractical this advice sounds for anyone who has not yet arrived at the top.

Anybody who has worked in large organizations will recognize how few genuinely good choices there are if you want to make family a priority and still remain on the fast track. Every task turned down is a risk. Ask the boss to send someone else to that meeting in San Francisco? That feels like a form of asking to be replaced. And what if next time the boss doesn’t even ask?

Women could turn to their household partners for help if these partners weren’t mostly still at work. A 2010 report from the Center for American Progress explained that professional women exiting the workforce for family responsibilities is best understood as a reaction to “the labor market patterns of men rather than women.”

About 38 percent of professional men work 50 or more hours a week. In a study of “high earners,” 45 percent of them who worked for big global companies put in more than 60 hours a week.

And let’s be clear on this point: It’s still mostly women who scale back careers when the wall gets hit. According to the American Progress report, “having a husband who works more than 50 hours a week increases the odds of a woman quitting her job by 44 percent. Having a husband who works more than 60 hours a week increases her odds of quitting by 112 percent.”

Only 6 percent of families had both parents working 50 hours or more per week. The surprising thing is that many families managed it.

You hear from professional people that a long week as a product manager or associate general counsel is just the price of accepting highly compensated work in highly competitive fields.

But it seems equally valid to think of overwork as a cultural trait, in companies and in the broader business community. Looking to the top of an organization for help on this is often no solution at all, because whoever got to the C-suite did so in part by outworking their peers. And there’s data that shows that men in senior leadership are more likely than their colleagues to have wives looking after home.

Hopefully the national conversation happening this month after the publication of “Lean In” will lead to some practical changes in workplace culture. In a memo leaked earlier this month, Cisco Systems CEO John Chambers told his leadership team that Sandberg’s book was required reading and that they had to prepare three or four specific ideas for what they as managers are going to do differently.

Sandberg thinks that just having more female senior leaders will lead to changes in workplace rules and expectations. After all, when working for Google she marched into the office of Google’s co-founders to insist that parking places near the front door be reserved for pregnant women.

It would be interesting to learn if she has ever insisted that her current boss get rid of his neon lockdown sign.