The strategy of stupid
Microsoft has repeatedly demonstrated the right way to move into the future: make the big paradigm shifts optional, and allow users to adopt them at their own pace.
They did it with the shift from command-line DOS to GUI Windows. The latter ran on top of the former (quite nicely) for a decade or more, allowing users to use both modes as they needed. Even when the DOS underpinning was removed, the DOS box maintained backward compatibility elegantly and conveniently.
They did it again with the shift from the Win 9x codebase to the far more sophisticated NT codebase. The two versions of Windows coexisted happily for nearly a decade. (We've recently discovered that Windows 3.x is still doing its job out in the field, in some pretty major applications. That kind of longevity is a good thing, except maybe to corporate bean-counters.)
But Ballmer and Nadella forgot those brilliant examples. They decided, quite wrongly, that the way to embrace mobile was to mutate the core OS and bludgeon users into coming along. Even Apple wasn't that arrogant. This strategy will fail, not because users hate it (which they do), but because it's not technically feasible. It's one of those software feats that looks workable, but in practice breaks down for a million small reasons.
For example, Microsoft may be able to squeeze Windows 10 onto mobile devices, but those devices will never be as mobile as those running a dedicated mobile OS. It's like Achilles and the Tortoise: by the time the Surface is as thin as an iPad, the iPad will be as thin as a sheet of paper. An awkward hybrid, Windows 10.x is guaranteed to always be second-best. Not to mention buggy, unusable and un-maintainable. (Linux is already vastly easier to install and service, and the gap is widening, not shrinking.)
Microsoft has become IBM. It seemed inconceivable in the early 1990s that there could ever be a microcomputer world without IBM as a significant force in it. But all it took was a few bad strategic choices - choices that were probably not as dumb as those Microsoft is making today.