Unless you've been living on Walden Pond for the last two decades, you know Serena Williams: She's won the most Grand Slam titles in singles, doubles, and mixed doubles combined among active players. She's been ranked #1 on eight separate occasions. She's won four Olympic gold medals. She's... well, shoot.

She's Serena.

And now she's also a mom. (A mom whose postpartum complications spotlights the dangers of childbirth, especially for black women.)

And she has some advice for her daughter.

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Earlier in her career, she says she let the stress of the game -- and especially of her own expectations -- negatively impact her performance. 

"I had lost every Grand Slam that year," she said in a CNBC interview. "I was in the U.S. Open, and Patrick (Mouratoglou), my coach, said, 'Serena, this doesn't make sense. You're so stressed about 18." (Winning 18 Grand Slams would tie her with Chris Evert and Martina Navratilova, two legends of the game.) "Why not 30? Why not 40?'"

In that moment she realized that the key to success didn't lie in comparing herself to others -- the key to success was to simply compare herself to herself.

"Why would I want to stand side by side when I can stand out on my own?," she said. "I think sometimes women limit themselves. I'm not sure why we think that way, but I know that we're sometimes taught to not dream as big as men, not to believe we can be a president or a CEO, when in the same household, a male child is told he can be anything he wants."

And that's what she wants to pass on to her daughter.

"I'm so glad I had a daughter," she said. "I want to teach her that there are no limits."

That's the approach nearly every successful person takes that I interviewed for my new book, The Motivation Myth: How High Achievers Really Set Themselves to Win. (Including, it should come as no surprise, her sister Venus.) 

Successful people don't compare themselves to others; they focus on becoming better tomorrow than they are today. They know that if you're willing to work hard and persevere, who you are is more than enough.

Never measure yourself against other people. Pick a goal for yourself, and measure yourself against that goal. That's the only comparison that matters.

Stop looking back. Start looking forward to see how far you can still go. Start comparing your present self -- regardless of how far you think you have already come -- to what is actually possible. 

And then work hard to get there.

You may never be as talented as the absolute best in the field or pursuit you choose ... but you will definitely achieve much more than your self-imposed limits allowed you to think was ever possible.

And you just might find that there really are no limits to what you can achieve.