Warren Buffett started reading books about investing when he was just 7 or 8 years old. His father owned a small investment shop, and young Buffett often picked up the books lying around the office.
By the time he was 11, Buffett was going to the local public library in Omaha and reading every book he could find on the topic.
One book in particular stood out. The billionaire now says "The Intelligent Investor" changed his life. The investing manual was written by former Columbia Business School professor Benjamin Graham and first published in 1949.
"I knew what everybody thought and all of that at an early age, but what Graham wrote made sense," says Buffett, speaking at a recent Facebook live event broadcast from Columbia University and moderated by Charlie Rose.
"I just happened to pick up that book up at a bookstore in Lincoln, Nebraska," he says, noting that he was only age 19 at the time.
In the book, Graham details his philosophy of "value investing," or buying stocks when they are undervalued and holding them for a long period of time. This would later become a hallmark of Buffett's investment strategy.
"Intelligent investment is more a matter of mental approach than it is of technique," writes Graham. "A sound mental approach toward stock fluctuations is the touchstone of all successful investment under present-day conditions."
Indeed, Buffett, now the chairman and CEO of Berkshire Hathaway, says that what makes him a good investor is his even temperament.
That, and he isn't useful for much else, he jokes.
"I certainly wasn't going to be a pro football player," Buffett says with a laugh. "It was a question of zeroing out all the other incompetencies, and I was left with one thing."