Bill Gates reveals his 'greatest mistake' that potentially cost Microsoft $400 billion

Bill Gates, co-founder of Microsoft, during an interview at the World Economic Forum in Davos, Switzerland, on Jan. 22, 2016.
David A.Grogan | CNBC | NBCUniversal | Getty Images

You might assume that as the second richest person in world with a net worth of $107 billion, Bill Gates doesn't have a lot of regrets. But there is a big one that still eats away at him, he says.

Gates admitted his "greatest mistake ever" was allowing Google to develop Android — one of Apple's biggest smartphone competitors — before Microsoft could develop a competing mobile operating system, he told Eventbrite co-founder and CEO Julia Hartz Thursday at a Village Global event.

"That was a natural thing for Microsoft to win," he said.

Gates said he blames his own poor "mismanagement," since he didn't guide his team to jump on the opportunity. He also partially blames Microsoft's antitrust problems in the early 2000's for allowing Google to get ahead.

Google moved on mobile shortly after Apple did, when it acquired Android in 2005. Google later released it first Android device in September 2008, a little more than a year after Apple released its first iPhone on June 29, 2007.

"These are winner-takes-all markets. So the greatest mistake ever is whatever mismanagement I engaged in that caused Microsoft not to be what Android is," he said.

Gates added that there is now only room for one "non-Apple" operating system, and that market is worth $400 billion, he said.

He added that if Microsoft would have "got that one right," Microsoft would be the top technology company in the game right now.

"We would be the company. But oh well," he said.

Despite Gates' blunder, Microsoft still currently has the highest market cap of the contenders at $1 trillion; Apple currently has a market cap of $918 billion, with Alphabet Inc. (the conglomerate which owns Google since 2015) coming in at $776 billion.

"It's amazing to me, having made one of the greatest mistakes of all time...our other assets — Windows, Office — are still very strong. So we are a leading company," he said.

Correction: This story has been revised to correct that Google acquired Android in 2005.

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