Launching a billion-dollar business or rising to the top of the C-suite requires making some sacrifices, and oftentimes, downtime can be in short supply. CEOs are divided on how they feel about work-life balance, but many seem to take issue with the concept itself—and Amazon founder Jeff Bezos is set on redefining the notion on his own terms.

“I don’t love the word ‘balance’ because it implies a tradeoff,” Bezos said recently at Italian Tech Week. “I’ve often had people ask me, ‘How do you deal with work-life balance?’ And I’ll say ‘I like work-life harmony because if you’re happy at home, you’ll be better at work. If you’re better at work, you’ll be better at home.’ These things go together. It’s not a strict tradeoff.”

It’s not the first time the entrepreneur worth $240 billion has struck back against the idea. In 2018, Bezos called work-life balance a “debilitating phrase” for the same reason: it implied that one has to give, in order for the other to thrive. Instead, he likes to use the word “harmony” and likened the concept to a “circle.”

And he’s not the only CEO who views their work and personal lives in the same way; Microsoft CEO Satya Nadella also thinks that “work-life balance” isn’t the goal, but rather “harmony” is the objective. Meanwhile, Nespresso’s UK CEO Anna Lundstrom aims for “work-life fluidity” because she doesn’t believe separating the two in half is possible when you’re at the top.

But not all leaders see work and life as complementary. Some set strict boundaries, others blur the lines entirely, and many are mindboggled by the concept entirely.

Andrew Feldman, CEO of $8.1 billion AI chip company Cerebras

There are many workers out there who are perfectly happy clocking in at 9 a.m., and heading out the door at 5 p.m.—and Cerebras cofounder and CEO, Andrew Feldman, said they can have a “great life.” However, if they want to launch the next billion-dollar company or innovative product, they won’t get far working 40 hours per week.

“This notion that somehow you can achieve greatness, you can build something extraordinary by working 38 hours a week and having work-life balance, that is mind-boggling to me,” Feldman, leader of the $8.1 billion AI chip company, stressed recently on the 20VC podcast. “It’s not true in any part of life.”

“The path to build something new out of nothing, and make it great, isn’t part-time work. It isn’t 30, 40, 50 hours a week. It’s every waking minute. And of course, there are costs.”

Lucy Guo, cofounder of $29 billion tech company Scale AI

Lucy Guo, the cofounder of Scale AI, knows what it takes to make it to the top. She’s a college dropout who put all her time and energy into building up the unicorn company, frequently waking up at 5:30 a.m. and ending her day at midnight. At just 30 years old, she became a self-made billionaire thanks to her 5% stake in the company, now valued at $29 billion.

“I probably don’t have work-life balance,” Guo told Fortune earlier this year, adding that those who crave it are simply in the wrong job. “For me, work doesn’t really feel like work. I love doing my job…I would say that if you feel the need for work-life balance, maybe you’re not in the right work.”

But she does have a concession: even when she’s clocking in 90-hour workweeks, Guo still finds a spare hour or two to connect with friends and family. The entrepreneur advises that everyone should always make time for the special people in their lives, “regardless of how busy you are.”

Eric Yuan, CEO of $22 billion software company Zoom

Eric Yuan is leading a $22 billion software company with a product used by millions of white-collar professionals around the world: Zoom. The tool has enabled employees to work and connect with their teams from virtually anywhere, breaking down the barrier between professional and personal lives.

But since becoming the cornerstone product of remote and hybrid working, and reaching new heights of success in the process, its chief executive said achieving that true work-life balance is difficult—and that he’s even given up hobbies to focus on work.

“I tell our team, ‘Guys, you know, there’s no way to balance. Work is life, life is work,’” Yuan said during an interview with the Grit podcast earlier this year.

But in moments when he’s forced to prioritize work or life, the former will always take the backseat: “Whenever there’s a conflict, guess what? Family first. That’s it.”

Reid Hoffman, cofounder of $26.2 billion social media giant LinkedIn

Other CEOs take a much harsher stance on the concept of work-life balance. Linkedin cofounder Reid Hoffman believes that if you’re serious about starting a company, you should say goodbye to binge-watching your favorite Netflix show after dinner or sleeping in on the weekends—you need to be on the work grind all hours of the day.

“If I ever hear a founder talking about, ‘This is how I have a balanced life,’ they’re not committed to winning,” Hoffman told Stanford University’s How to Start a Startup class in 2014. “The only really great founders are [the ones who are] like, ‘I am going to put literally everything into doing this.’”

Jack Ma, cofounder of $338 billion company Alibaba

America isn’t the only country with a “grindset” culture. China is also famous for its “996” schedule, where workers are clocking in from 9 a.m. to 9 p.m., six days a week. It’s a demanding schedule that most employees would gawk at—but Jack Ma, the cofounder of $338 billion e-commerce giant Alibaba, said the 72-hour workweeks are godsend for staffers.

“I personally think that being able to work 996 is a huge blessing,” Ma said on Alibaba’s WeChat account in 2019.

“Many companies and many people don’t have the opportunity to work 996…If you don’t work 996 when you are young, when can you ever work 996?”

Are you an executive, founder, or CEO who has strong thoughts on work-life balance, and whether or not it’s attainable? I’d like to hear from you! Reach out at emma.burleigh@fortune.com

Billionaire bosses like Jeff Bezos and Reid Hoffman denounce work-life balance—and some think working nonstop is key to success