Anthony Au-Yeung/Getty ImagesCaroline Wozniacki is one of the top tennis players in the world. 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.