The Android fragmentation boogeyman.
What nobody's ever explained to my satisfaction is why I should give a flying f*ck. As far as I can see "fragmentation" is simply the result of users and developers not all being forced to upgrade to the latest and greatest when the platform vendor demands it. This is actually a *good* thing.
It means I can find a $40 Android tablet running KitKat, which is perfectly fine for things I want to use a $40 tablet for. I'm out of the developer business now, but I still dabble to keep up with developments, and far as I can see the Google tools do a really nice job of allowing developers to target a range of platforms and still look up to date on the latest and greatest. So I don't have to shut out people who bought a smartphone last year if I want to use Material Design (which is cartoony for my taste but does a nice job setting out consistent UI guidelines).
If this is fragmentation hell, all I can say is come on in, the the lava is fine. Sure it would be *nice* if the adoption rate for the latest and greatest was higher, but as a long time user and developer I have to say that not being pushed over the upgrade cliff on the platform vendor's orders is nice too.