(Reuters) – The Oracle of Omaha, Warren Buffett, admitted on Monday he knew less than he thought about Oracle Corp, the company overseen by fellow billionaire Larry Ellison.

Investors were flummoxed earlier this month when Buffett’s company, Berkshire Hathaway Inc, revealed that during last year’s fourth quarter it had exited a $2.13 billion stake in Oracle that it had taken the prior quarter.

It is rare for Berkshire, which owns some stocks for decades, to unwind an investment so fast. It is also rare for Berkshire to make large investments in the technology sector.

Speaking on CNBC television, Buffett recalled his unsuccessful investment in International Business Machines Corp in determining that Oracle, the company, wasn’t for him, though Ellison had done a “fantastic job” running it.

“After I started buying it, I felt I still didn’t understand the business,” Buffett said. “Particularly after my experience with IBM, I don’t think I understand exactly where the cloud is going.”

The Oracle of Omaha is a nickname that Buffett’s fans often use for him. His conglomerate is based in Omaha, Nebraska.

Berkshire said it ended the year with $172.8 billion of stocks, including $40.3 billion in iPhone maker Apple Inc, which Buffett views more as a consumer company.

He said the total may rise in 2019 because it has become tough to buy whole companies to add to Berkshire’s portfolio of more than 90 businesses, including the Geico auto insurer and BNSF railroad.

It is unclear why Berkshire’s annual report on Saturday omitted a previously included section called “acquisition criteria,” including that Berkshire preferred “simple businesses (if there’s lots of technology, we won’t understand it).”

Buffett and longtime Vice Chairman Charlie Munger ceded day-to-day oversight of Berkshire’s operating units last year to Vice Chairmen Greg Abel and Ajit Jain.