Venus Williams says the best advice she ever heard came from 17-year-old Serena Williams

Venus and Serena during a doubles match at the 1999 US Open
Bernie Nunez | Getty Images

At the 1999 U.S. Open, both Venus and Serena Williams reached the semifinals on opposite sides of the draw. Venus was 19 and her sister was 17.

"We were kids," Venus recalled at a Q&A with American Express executive Susan Sobbott this week.

The night before the sisters played their semifinals, Venus asked: "'So, Serena, are you nervous about tomorrow?' And she's like, 'No, I'm not nervous because we have to show up. And since we have to show up, why not compete?' And that was the best advice I ever got in my life."

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"Sadly, I didn't listen to it at the time," added Venus, who lost in a third set to top-seeded Martina Hingis. "That was one of my first biggest failures, and it was my biggest lesson, and my whole career changed after that."

Since, Venus has won seven Grand Slam singles titles, including the 2000 U.S. Open. The 37-year-old is not only still competing today, but currently ranked No. 5 in the world.

The 1999 loss to Hingis has contributed to her success today. "Everything makes you stronger if you allow it to," Venus told CNBC in an episode of Life Hacks Live.

"Of course, I would love to mow down all my opponents and have all the wins ... but that's not always the case. And it's all those other moments, the obstacles and challenges, that make you greater."

Nearly 20 years after the memorable 1999 U.S. Open, Venus still says her kid sister's advice is the best she's ever heard. "You have to show up, so why not compete? ... It just never gets old," Venus told Sobbott.

And if you were wondering, the mindset worked for 17-year-old Serena. The teen won her semifinal and then went on to defeat Hingis in the U.S. Open final to clinch her first of 23 Grand Slam singles championships.

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