Master Class

Kevin O'Leary: If you want to get rich, start working 25 hours a day, 7 days a week 

Kevin O'Leary: Get ready to work 25 hours a day to become successful in business

Everybody seems to be striving for work-life balance. But if you want to be an entrepreneur, especially one who's rich and successful, that's not an option — you have to be prepared to work very hard, says financial expert and star of ABC's "Shark Tank" Kevin O'Leary.

"If I have to give one piece of advice to someone who's thinking about starting a business, I tell them this: Forget about balance," O'Leary tells CNBC's Make It. "You're going to work 25 hours a day, seven days a week, forever.

"That's what it takes to be successful."

You're going to be competing with tons of determined people who "want to kick your ass. It's a job 24-7," he continues.

"Get over it, and get ready for it."

O'Leary isn't the only money mogul to recommend a rigorous work schedule. Self-made millionaire Grant Cardone has said that while most people work 9 to 5, he works 95 hours per week, and if you ever want to be a millionaire, you need to do the same.

For his part, O'Leary is an expert at hustle and hard work. He typically wakes up at around 4:30 a.m. and juggles his many ventures, from managing his "Shark Tank" investments to lecturing at universities to running a number of his own businesses.

When it comes to investing in other entrepreneurs, he doles hundreds of thousands of dollars on "Shark Tank" each season, but only when he's convinced they'll work extremely hard to be successful.

"The biggest myth of being an entrepreneur is that you're going to get rich overnight," O'Leary says. "It practically never happens. Most people slog it out for years, and sometimes even decades."

Still, O'Leary also says that when it comes to entrepreneurship, money shouldn't be the motivating factor. What should keep you going through those long weeks and rough patches is the pursuit of personal freedom. And that's what you should focus on.

"It's a long, hard journey, but it's worth it," O'Leary says. "It's not about the greed of money, it's about the pursuit of personal freedom. If you're successful as an entrepreneur, you will set yourself free, and that's worth fighting for."

Don't miss: Here's the mental trick this introverted Duolingo exec uses to lead effectively

Like this story? Subscribe to CNBC Make It on YouTube!

Rent the Runway COO: This is the key to success in business (and life)