Tennis icon Serena Williams says people need to grind “every day” and be “determined” to make it big, whether it’s in sports or business. The 43-year-old, who is now leading her own VC firm Serena Ventures, is investing in and mentoring underrepresented founders, with her principal piece of advice being to “show up 28 hours out of 24” hours in a day. Other successful leaders like Brian Niccol, Steve Jobs, and Mark Cuban have previously echoed her sweat equity work ethic.

It’s an old adage that practice makes perfect—something tennis star Serena Williams knows all too well. She echoes the sentiment that the grind never stops on the path to success, in both her athletic and business endeavors. Persistence and determination are two winning traits for sweeping a match—or leading an entrepreneurial venture.

“Tennis is [played] every day, you have to do it every day. You have to train, and business is the same,” Williams told CNBC Make It in a recent interview. “It is exactly the same. You have to be very disciplined.”

“You also have to be determined through ups and downs, be determined to keep going.”

Williams has won 23 Grand Slam titles throughout her 27-year stint as the darling of tennis; in 2022, the Olympic athlete decided to step away from sports to focus on her business work. She started a capital fund called Serena Ventures in 2014, where she uplifted diverse entrepreneurs, boasting that its Fund 1 investments were 79% underrepresented founders, 54% women founders, 47% Black founders, and 11% Latino founders. Serena Ventures raised $111 million during its early-stage fundraising—now, she says her portfolio includes more than 14 billion-dollar companies and several decacorns.

Williams’ new career with Serena Ventures is budding as she helps uplift startup leaders and small businesses, like wig-customization platform Parfait, independent publication Wonderland, and relationship-wellness company Ours, to reach new heights.

“That’s one thing that I’m excited to do, is to talk to these mentors about that determination that I’ve shown so much in my past career and just bring it out to this new career,” Williams said.

Fortune reached out to Williams for comment.

Serena’s advice: working 28 hours a day and staying humble

Williams tells Fortune she’s drawn to founders who have a personal root to the problem their company is trying to solve. And when it comes to advising them on leading a successful business, the decorated tennis champion says people need to go above and beyond.

“When I mentor founders one thing that I find myself giving over and over again is to just dust yourself off and don’t stop,” Williams told Fortune in a recent interview. “VC is interesting—it’s a tough business, and then as a founder starting a new company, you have to show up 28 hours out of 24.”

“You win a few, you lose a few. You get knocked down, and you get right back up.”

Williams displayed that same grit in her career, setting tennis records that may never be broken. With 367 career wins, 319 consecutive weeks as the number-one tennis player, and nearly $95 million in total prize money, the 43-year-old legend should feel on top of the world. But even in the heights of her success, she’s stuck to a philosophy that brings her down to earth.

“I think the main value that they instilled in me is just humility, and I think that goes way better than any championship or anything, because it keeps you grounded as an individual,” Williams told CNBC. “It keeps you respectful, and it keeps you just like everybody else, because at the end of the day, we’re all the same.”

Other successful leaders staying humble and curious

Williams isn’t the only successful person espousing the idea of grinding all hours of the day. As a huge proponent of “sweat equity,” serial investor Mark Cuban has recommended to “work like there is someone working 24 hours a day to take it all away from you.” And late Apple cofounder Steve Jobs, who started working at Hewlett-Packard at the age of 13, said the determining factor between successful and unsuccessful entrepreneurs is “pure perseverance.”

Brian Niccol—the CEO of Starbucks, formerly holding prominent roles at Chipotle, Pizza Hut, and Taco Bell—also stays grounded by being curious. Despite being at the helm of a $111 billion coffee giant, Niccol doesn’t see himself as having all the answers. Employees of all rankings still have something to teach him.

“The best business advice I ever received was: ‘Don’t be afraid to ask questions,’” Niccol told Fortune last year. “Regardless of what position you’re in, even as the CEO, there are moments where somebody’s talking about something, [and] I don’t totally get what they’re talking about.”