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Caroline Wozniacki.
She's had endorsement deals with major companies from Adidas to Godiva, and she made Forbes' list of highest-earning female athletes for 2016, with a reported $8 million of earnings between June 2015 and June 2016.
But she still uses the money advice her father gave her as a child.
In a letter to her younger self published on The Players' Tribune and republished on Business Insider, Wozniacki recalls early-morning car rides to the tennis club with her dad.
"Over and over again as you're growing up, Dad will press you to think hard about what it is you love to do, or what you enjoy spending time on, and then - regardless of what the answer is - he will encourage you to make a plan for how to be successful at it," she writes.
One of those things that requires a plan is money. She writes:
"When you sit down with him as a young woman to talk about your financial future, and you tell him that you have always been fascinated by real estate, that will be music to his ears. Because you will travel so much for tournaments, and will always be moving from one place to the next, you will love the idea of owning land, and a beautiful home where you can feel truly relaxed.
"Dad will get that, and because he's always warned you about the dangers of high-risk investments, he'll be excited to hear about your interest in something more secure. 'If you're smart,' Dad will say, 'You will always, at the very least, know that you'll have a roof over your head.'
"He'll help you to fully understand the value in being prudent, and in making sure you have a safety net. Dad will preach the importance of not making bad decisions that could impact the lives of your children and their children. 'You can secure your family for generations if you're careful,' he'll tell you. And he's right about that.
"So there will be no mega-yachts in your future. No jetpacks. No Fabergé eggs."
However, she continues, she'll allow herself to do some spending. Specifically: a Ferrari. But only one. "Not six," she writes. "And not a Rothko original, or any sailboats. No random expensive things." She continues:
"You've got to really love something you spend a ton of money on, Caroline.
"But if you do, and if you've thought it through, and you can make it work without doing any long-term damage to your finances, then it's O.K. to reward yourself sometimes.
"And you love that car.
"So buy it. You're human. And you've worked exceptionally hard. You can give yourself that present.
"Then go back to being frugal again for a while. And along the way, always remember those business lessons from Dad that date all the way back to the car rides to the tennis club at six in the morning."