Warren Buffett says the most important decision you'll ever make has nothing to do with your money or career

Warren Buffett (L), chairman and CEO of Berkshire Hathaway, arrives with his first wife Susan at the White House for a state dinner on Feb. 5th, 1998.
Chris Kleponis | Getty Images

Berkshire Hathaway CEO Warren Buffett has made his fortune through smart investing. But if you asked the self-made billionaire about the most important decision he has ever made, it would have nothing to do with his investments.

In HBO's 2017 documentary, "Becoming Warren Buffett," the investing legend says the biggest decision of your life will be who you choose to marry.

There have been "two turning points" in his life: "One when I came out of the womb and one when I met Susie," Buffett says of his first wife, who died in 2004. "What happened with me would not have happened without her."

Why the secret to your success is who you marry
Why the secret to your success is who you marry

Buffett addressed the topic during a 2017 conversation with Bill Gates at Columbia University, too. "You want to associate with people who are the kind of person you'd like to be. You'll move in that direction," he said. "And the most important person by far in that respect is your spouse. I can't overemphasize how important that is."

That's life advice the 87-year-old has been emphasizing for years. As he said at the 2009 Berkshire Hathaway annual meeting, "Marry the right person. I'm serious about that. It will make more difference in your life. It will change your aspirations, all kinds of things."

Research agrees that who you marry can significantly affect your level of success. People with supportive spouses are "more likely to give themselves the chance to succeed," according to a study published by psychologists from Carnegie Mellon University.

Another study by Brittany C. Solomon and Joshua J. Jackson of Washington University in St. Louis shows that having a conscientious spouse can boost your salary by $4,000 per year and increase your chances of getting promoted.

"Significant others can help you thrive through embracing life opportunities," Brooke Feeney, lead author of the Carnegie Mellon study, tells CNBC Make It. "Or they can hinder your ability to thrive by making it less likely that you'll pursue opportunities for growth."

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