Ninety-year-old billionaire Warren Buffett reaffirmed his fervent belief in the American Dream in a letter to investors published Saturday -- advising them never to bet against the country despite its many problems.

"In its brief 232 years of existence, there has been no incubator for unleashing human potential like America," he said in the message to investors in his Berkshire Hathaway conglomerate.

Even after a particularly difficult 2020 -- when the Covid-19 pandemic plunged the world's largest economy into recession and pushed millions into poverty -- "our country’s economic progress has been breathtaking," he said.

The man known as the Oracle of Omaha added: "Our unwavering conclusion: Never bet against America."

Buffett's annual letter is always highly anticipated by the business world because of his reputation as a prudent investor with a canny view to long-term trends.

But in his latest letter, Buffett did acknowledge a mistake made in 2016 that became evident last year: Berkshire's purchase of Precision Castparts (PCC), which led to an "ugly $11 billion write-down."

"I paid too much for the company," Buffett wrote. "No one misled me in any way –- I was simply too optimistic about PCC's normalized profit potential," an error laid bare when the company's aerospace customers fell on hard times last year.

Buffett also announced that Berkshire's annual meeting, which in normal years draws thousands of shareholders to Omaha, Nebraska will take place in a virtual format on May 1, as it was last year because of the pandemic.

He said he and partner Charlie Munger would answer shareholders' questions.

Last year, Buffett wrote, the conglomerate they led met neither of two goals: "Berkshire made no sizable acquisitions and operating earnings fell nine percent.

"We did, though, increase Berkshire's per-share intrinsic value by both retaining earnings and repurchasing about five percent of our shares."

He voiced confidence that Berkshire’s capital gains from its investment holdings would be "substantial" over time.

Looking ahead, Buffett said Berkshire would remain "a collection of controlled and non-controlled businesses."

He said shareholders' capital would be invested in "whatever we believe makes the most sense, based on a company’s durable competitive strengths, the capabilities and character of its management, and price."

Berkshire had net earnings in 2020 of $42.5 billion, helped by its insurance business, but the overall figure was down 48 percent from 2019.

Berkshire last year sold its airline stocks because of the pandemic and invested more heavily in pharmaceutical products.