He had achieved his childhood goal of assured financial independence.
Everything after that, he explained in a talk at Ivey Business School in late February, "has been surplus."
Today at age 84, he is the world's third wealthiest person, with an estimated net worth of over $70 billion, and has cemented his reputation as one of the greatest investors in history.
In the Ivey talk, Buffett was asked about his personal definition of success. He explained that he's been motivated by an inner drive to feel proud of his work and to continue improving his business, which has been the Berkshire Hathaway conglomerate since 1970.
"The saying goes that success is about getting what you want, while happiness is about wanting what you get," he said. "For myself, happiness is more important."
Buffett advised not to judge yourself and your performance by what other people think.
"As you move along in your career, you always want to consider your inner scorecard — how you feel about your own performance and success," he said. "You should worry more about how well you perform rather than how well the rest of the world perceives your performance."
Buffett has always prioritized the success of his company over his own personal success in terms of financial returns, he said, which may be why he tells his management team that their top priority is to "zealously guard Berkshire's reputation."
According to Buffett, true success comes from working for a purpose greater than your own well-being.
"The most important takeaway is that you should always try to be a good person," he said.
