In 2008, Mohnish Pabrai and Guy Spier paid $650,100 for a charity lunch with Buffett. Spier, a hedge fund manager based in Zurich, later recalled the meal in his 2014 memoir, The Education of a Value Investor, which I helped him write.

What stood out most for him from this three-hour masterclass with Mr. Buffett was one life-changing piece of advice.

“It’s very important,” said Mr. Buffett, “always to live your life by an inner scorecard, not an outer scorecard.”

Mr. Buffett illustrated this by asking: “Would you prefer to be considered the best lover in the world and know privately that you’re the worst—or would you prefer to know privately that you’re the best lover in the world, but be considered the worst?”