Microsoft’s never been particularly successful in the mobile industry. Its global dominance with desktops and laptops running Windows just never transferred over to phones and tablets. The reasons may seem obvious, but the company has stayed quiet on what actually went wrong in making a successful mobile operating system. That’s until now as the man who led Windows for several years is leaving the company, and he’s shared a postmortem on his way out the door.

Terry Myerson, who’s leaving Microsoft after two decades of service with the company, has revealed what caused Windows Phone to lose to iOS and Android.

Windows Mobile was the company’s mobile operating system for around a decade when Microsoft decided to take on Apple and Google, but by then it was too late. Both iOS and Android had already grown globally with the latter earning support from plenty of third-party manufacturers.

Microsoft was never able to stand out. Myserson says creating Windows Phone was “incredibly challenging” because, although the experience was unique, Android was a disruptor in the industry. Google developed the software but let others handle hardware.

Here’s why he believes the company fell behind:

“We had a differentiated experience, but it’s so clear in hindsight that the disruption in business model which Android represented was enormous, and that building our early versions of Windows Phone on an incomplete Windows CE platform, designed for small embedded systems, left us too hobbled to ever catch up.”

Based on that statement, it would seem Microsoft struggled to juggle both hardware and software. The company couldn’t develop Windows Phone fast enough, so its familiar partners from the PC industry looked to Android. By the time Windows Phone was prepared as a full-blown mobile operating system, consumers were entrenched in iOS and Android.

The only brand to embrace Windows Phone ended up being Nokia, which Microsoft acquired in 2013 to bolster hardware production. Neither side benefitted from the deal as Windows Phone stood no chance at being revived and Nokia’s name was retired.

Shortly after, Windows Phone was rebooted as Windows 10 Mobile. But, again, no one showed any interest. Microsoft finally decided to end development in October 2017.

What’s next for Myerson is unknown, but we have an idea of Microsoft’s strategy for phones and tablets. The company isn’t interested in rolling out phones or tablets, the Surface Pro being an exception for the latter. Microsoft instead wants to focus on creating software that works perfectly between computers and mobile devices.