For decades, one question has fueled the debate over whether women can balance the demands of career and motherhood: can women "have it all"? 

"All" has become shorthand for women who excel in their personal and professional lives, who can be a great mother or partner and have a thriving career at the same time — an equilibrium that feels increasingly out of reach as women face mounting economic and personal pressures.

The notion that women can have it all is the "biggest lie" working women are told that, if believed, can stunt their success, according to Bonnie Hammer, vice chairman at NBCUniversal.

In her new book, "15 Lies Women Are Told at Work," Hammer explores the conflicting advice women are given regarding professional success. 

Having it all is a "wrong and dangerous" ideal for women to aspire to, the 73-year-old tells CNBC Make It. 

The pressure alone to achieve everything on your personal and professional bucket list is enough to leave women feeling "stressed, dissatisfied and burned out," she explains. "Even if we succeed on all fronts, there's very little chance we have time left for ourselves." 

Women have reported higher levels of burnout than men for years, a gap that has more than doubled since 2019, Gallup reports. 

The widening gap can be boiled down to gender inequities: Research has found that women are less likely to be promoted than men yet more likely to head single-parent families and take on unpaid labor – all things that can exacerbate burnout.

Soaring child-care costs are also driving women out of the workforce. 

Another issue with "having it all" is that "all" has become a blanket term referring to parenthood and professional success, which may not appeal to every woman, Hammer points out.

"You can't have it all if the benchmarks don't feel right or motivate you," she adds.

Hammer suggests that women define what their "all" looks like and understand that the definition won't be fixed or immutable. 

Your "all" should be a list of what you need, want and would love to have to live a happy life. If your list is long, rank the items on it. 

If two items conflict with each other (like taking more vacations and spending more time at the office), try to figure out which item is more important to you "right now," says Hammer, and plan to revisit the second goal later.

"It's draining to try and excel in all aspects of your life, no one has the time or energy for that," she says. "Instead, choose a few goals to focus on, identify where you need support and don't feel guilty about the things you need to let go."

"You will always feel off-balance, and that's normal," she adds. "Your 'all' will change and look different from your friend or co-worker's 'all.' Embracing that can help you feel more confident and in control of your life."

Disclosure: NBCUniversal is the parent company of CNBC.

Want to land your dream job in 2024? Take CNBC's new online course How to Ace Your Job Interview to learn what hiring managers are really looking for, body language techniques, what to say and not to say, and the best way to talk about pay. Use discount code NEWGRAD to get 50% off from 5/1/24 to 6/30/24.

Plus, sign up for CNBC Make It's newsletter to get tips and tricks for success at work, with money and in life.