Bill Gates has a resume of career highs, but he calls Microsoft’s failure to become Apple’s chief iOS rival his “greatest mistake.”

The Microsoft founder made the admission twice in recent interviews when discussing how Microsoft lost out to Google in launching a mobile operating system to rival Apple’s iOS.

“In the software world, particularly for platforms, these are winner-take-all markets,” Gates said in a recent interview with venture capital firm Village Global. “So the greatest mistake ever is whatever mismanagement I engaged in that caused Microsoft not to be what Android is. Android is the standard non-Apple phone platform. … There’s room for exactly one non-Apple operating system.”

For years, Microsoft (MSFT) was the leader in the computer industry, beating Apple, but failed to evolve fast enough in the smartphone era. Microsoft came out with its own mobile operating system, called Windows Mobile, in 2000. Apple debuted its iPhone in 2007, followed by Google’s Android platform in 2008. While Microsoft had a mobile operating system first, it quickly fell behind Apple (AAPL) and Google(GOOG).

In an interview Monday at the Economic Club in Washington, DC, Gates said the antitrust trial it faced at the time was a major distraction. He also said the company failed in how it assigned staff to work on mobile.

“We knew the mobile phone would be very popular so we were doing what was called Windows Mobile. We missed being the dominant mobile operating system by a very tiny amount,” he said at the event. “We were distracted during our antitrust trial. We didn’t assign the best people to do the work. So it’s the biggest mistake I made in terms of something that was clearly within our skillset. We were clearly the company that should have achieved that — and we didn’t.”

The antitrust trial was the result of lawsuits filed by the US Department of Justice, 20 states and the District of Columbia accusing Microsoft of illegal, anti-competitive and exclusionary practices.

In the Village Global interview, Gates said the misstep potentially cost the company billions of dollars that ultimately went to Google. Android is the most popular smartphone platform in the US. In the first half of 2018, more than 85% of all global smartphones sold had an Android operating system, according to data from Statista.

“Our other assets like Windows and Office are still very strong, so we are a leading company,” Gates said in the interview. “If we had gotten that one right, we would be the leading company, but oh well.”

But this isn’t Gates’ only regret. In 2017, he said apologized for how the wonky Control-Alt-Delete function originally used to get into Windows computers wasn’t just a single key.

The company has also had other missteps, including Windows Vista — one of the most disliked versions of Windows — and Windows ME, which was highly criticized for being buggy. Zune music players were also a major bust. Microsoft CEO Steve Ballmer once famously called the iPhone “the most expensive phone in the world, and it doesn’t appeal to business customers because it doesn’t have a keyboard.” (CNN)

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