Both Berkshire Hathaway CEO Warren Buffett and business mogul Kim Kardashian West are wildly successful in their own spheres. But the pair have another thing in common as well: They agree that the best investment they’ve ever made is in themselves.

"Ultimately, there's one investment that : Invest in yourself," Buffett told Forbes. “Address whatever you feel your weaknesses are, and do it now.”

The legendary investor learned this lesson firsthand when he enrolled in a as a young adult, which he says changed his life. The course was taught by Dale Carnegie, the well-known author of “How to Win Friends and Influence People.”

"I was terrified of public speaking when I was young. I couldn't do it," Buffett says. He admits he became physically ill when the time came to take the podium. Still, he was determined to complete the course and master his fear. Not only did that make him a better investor and salesman, but he says he gained so much confidence that he during the course.