I think one fundamental miscalculation went like this: early adopters will start writing new code in python3, and it will gradually become more normal for new c

I think one fundamental miscalculation went like this: early adopters will start writing new code in python3, and it will gradually become more normal for new code to be python3, and eventually it will snowball and python2 will become legacy. The problem is that early adopters have a choice: python3, or a completely different language. And there are a lot of good languages to choose from, and early adopters are a more radical by nature. That's why breaking backwards compatibility is almost always worse than it looks like on paper: the early adopters you are counting on to get you through the transition are also the most likely to leave your platform completely.