My iPhone 6 Plus force upgraded itself to iOS 12 several months ago when I had to restore my phone. Unfortunately, my Apple Watch Series 0 or whatever you’ll call it only works with iOS 11. And now I won’t be able to upgrade my 6 Plus. So my two old devices will permanently and unnecessarily be incompatible with one another forever, through no action of my own (there was no way to avoid the iOS 12 “upgrade”).

Both will permanently be in the past, but one major version away from compatibility. It’s pretty frustrating.