Warren Buffett says he goes to bed more worried about another pandemic or nuclear war than his company

Warren Buffett says he can't do anything about "all kinds of things." Paul Morigi/Getty Images

• Warren Buffett says he worries more about nuclear war or another pandemic than his own company.
• He told CNBC "I never go to bed worried about Berkshire" Hathaway as he can always change something. 
• Buffett's friends including Bill Gates partly credit his success to his optimism and self-confidence.

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Warren Buffett said he worried more about the prospect of catastrophic global events than the success of his own company when he goes to bed at night.

The billionaire investor was asked during a recent appearance on CNBC's "Squawk Box" how much he fretted about economic factors such as recent bank failures and inflation. He said he was more concerned about things out of his control than issues with Berkshire Hathaway.

"Well, at 92 I've got other things to worry about," he told CNBC last week. "No, I don't worry about our ability. There's things I worry about. Sure. I worry about the nuclear threat. I worry about a pandemic in the future, all kinds of things but I don't worry about 'em because I can't do anything about 'em."

He continued: "I never go to bed worried about Berkshire and how we'll handle a thing. If I'm worried about Berkshire, I should figure out something different to do about what Berkshire is doing."

Buffett is known for his optimistic outlook, and friends like Bill Gates have credited his success to his ability to always find the bright side of a situation. In 2017, a data scientist analyzed decades of Buffett's annual letters to shareholders, and told CNBC he discovered common key words like "outstanding" and "excellent" that illustrated Buffett's ongoing optimism.

The billionaire also told CNBC that his general optimism and lack of concern about the company also stemmed from confidence in his own ability to identify risks and trends in the economy before others.

"I've got 99 and a fraction percent of my net worth in Berkshire, but I've got all my relatives in. I've got everybody in," Buffett said. "If I thought that I wasn't going to be able to do a decent job of managing the risk, a better than decent job, I'd be crazy to take on that responsibility."

He also said he believes happiness and optimism are important in living a long life, and that eating his favorite foods like burgers, ice cream, and Coca-Cola make him happy even if they're bad for him.