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

In a recent interview with Village Global, Bill Gates said: “In the software world, particularly for platforms, these are winner-take-all markets, 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.”

Talking about how the company failed in assigning “the best” staff to work on mobile, Gates, in an interview on Monday at the Economic Club in Washington, DC, said: “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,” CNN quoted Gates as saying 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 skill set. We were clearly the company that should have achieved that and we didn’t.”

For years, Microsoft 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 and Google

Bill Gates said that the misstep potentially cost the company billions of dollars that ultimately went to Google.