To me, the fragmentation of Linux as a platform, the multiple incompatible distros, and the incompatibilities across versions of the same distro were my Three Mile Island/Chernobyl.
Without noticing, I stopped turning on the screen for my Linux machine during 2012. By the time I moved to a new apartment in October of 2012, I did not even bother plugging the machine back and to this date, I have yet to turn it on.
Even during all of my dogfooding and Linux advocacy days, whenever I had to recommend recommended a computer to a single new user, I recommended a Mac. And whenever I gave away computer gifts to friends and family, it was always a Mac. Linux just never managed to cross the desktop chasm.