Even artificial intelligence wants to learn from Bill Gates.

When the Microsoft co-founder sat down for an interview with U.K. Prime Minister Rishi Sunak last month, the two answered questions generated by a ChatGPT-like AI chatbot.

The bot asked Gates about the best advice he’s ever received and how it has influenced his own life. In response, the 67-year-old pulled out some words from his longtime friend and fellow billionaire Warren Buffett on the subject of friendship.

“Warren Buffett talked about [how], in the end, it’s how friends really think of you and how strong those friendships are [that matters],” Gates said.

Gates and Buffett have been friends for more than three decades. Their shared interests go beyond their wealth: The pair co-founded The Giving Pledge, which encourages the world’s wealthiest people to donate at least half of their wealth to charitable causes, and are occasional bridge and golf partners.

Gates has previously discussed the lessons he’s learned from the 92-year-old Buffett, from investing to time management. He’s consistently put Buffett’s advice on friendship at the top of that list.

“I’ve learned many things from Warren over the last 25 years, but maybe the most important thing is what friendship is all about,” Gates wrote in a 2016 blog post.

“Even though he keeps up a hectic schedule, Warren still finds time to nurture friendships like few other people I know,” Gates added. “He picks up the phone and calls to say hello. He regularly sends articles he’s read that he thinks ... I will find interesting.”

Buffett often speaks about the importance of choosing good friends, and being a good friend yourself. That means surrounding yourself “with people that are better than yourself,” so you can learn from and be inspired by them, he said at a 2017 talk with Gates at Columbia University. “You will move in the direction of the people that you associate with.”

Gates agreed: “Some friends do bring out the best in you, and so it’s good to invest in those friendships.”

Strong and meaningful friendships can be quite important to your career success, including providing a boost to your self-esteem and mental resilience, research shows. Maintaining good friendships over the course of your life also makes you happier and less stressed, improving your health and well-being, according to the Mayo Clinic.

Gates and Buffett have a combined net worth of $220 billion, Bloomberg estimates, but they seem to agree that the happiness derived from lasting friendships is a true mark of success.

“When you get to my age, you’ll really measure your success in life by how many of the people you want to have love you actually do love you,” Buffett said in a 2001 speech at the University of Georgia.

“I know people who have a lot of money, and they get testimonial dinners and hospital wings named after them,” he continued. “But the truth is that nobody in the world loves them. If you get to my age in life and nobody thinks well of you, I don’t care how big your bank account is — your life is a disaster. That’s the ultimate test of how you have lived your life.”