The fizzling of OS/2 was as much IBM's fault as anything. If they'd paid more attention to it sooner, MS might never have shipped Windows; they'd just have made their office applications OS/2 GUI programs. But IBM was too fixated on its mainframes to realize that they were giving away the PC market to MS (again--they did it the first time by licensing DOS to MS).
Before Facebook, I used Friendster. Years later, I read how Friendster execs were too busy patting themselves on the back and flying around on private jets to get around to fixing the horrendous site lag of sometimes a minute to even sign into the web app. How could a company's leadership be so foolish? I understood this paled in comparison to the doomed arrogance of IBM's leaders when I read stories about IBM's downfall in the delightful book In Search of Stupidity: Over 20 Years of High-Tech Marketing Disasters.
Wait, did IBM license DOS to Microsoft? I thought IBM was looking for an operating system for the PC and approached Kildall about CP/M. That deal fell through, so they approached Microsoft. Gates didn't have anything, so he licensed QDOS for a song and licensed it to IBM.
I was being somewhat sloppy. IBM bought DOS from Microsoft for the IBM PC--but neglected to buy exclusive rights to it, so Microsoft could and did sell it on its own as MS-DOS. (And later, other vendors began selling their own versions.) For PC users, this was a great deal, since it effectively made the IBM PC an open standard. But it meant that IBM captured much less value from DOS and PCs than Microsoft did.