What Keeps Warren Buffett Up at Night? Hint: It's Not What You Think.

Warren Buffett, the icon behind Berkshire Hathaway (BRKA 0.17%) (BRKB 0.35%), is one of the best investors in human history. And he's worried about a lot of things. Last year, he told investors that he was increasingly worried about the U.S. budget deficit and debt load.

"I think the problem of how you control revenue and expenses in government is the one that is never fully solved and has really hurt dramatically ... many civilizations. And I don't think we're immune from it and we've come close to it," Buffett revealed.

"We are doing something that is unsustainable, and it has the aspect to it that it gets uncontrollable to a certain point," he added, noting that high levels of inflation, even higher than we've seen in recent years, could be the ultimate result.

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This is what Warren Buffett worries about most

Perhaps surprisingly, none of this keeps Buffett up at night. In 2015, he was asked directly: "Does anything keep you up at night?" Here's what he said:

The only thing that I ever feel badly about is friends or relatives having illnesses or deaths. You don't get over that, but nothing other than other people's -- or my own if I were feeling terrible -- discomfort or serious illness, or the extreme, being death. And as you get older you have more friends that die. ... [T]here's no great solution for how you feel about that. But nothing keeps me up at night. Never has.

Image source: Getty Images

Buffett's advise is characteristically wise. But it's also likely to be a product of his investing strategy. Buffett is notorious for his long holding periods, often investing in companies for "life." He's known for giving managers room to manage their respective businesses as they see fit, avoiding the allure of micromanagement. And his long-term business partners, such as Charlie Munger, often become close friends.

In short, Buffett probably isn't focused on what happens today, tonight, or even this week from a portfolio perspective. He's more interested in the long term. With that mindset in place, getting to sleep each night is likely to be an easier feat.