An important feature of SO is that it's been open: crawlable by search engines, readable by anyone without an account, etc.
In those same four years Facebook, Twitter and the likes of Quora have exploded, and made the Internet worse. Yet at the same time all the Stack Exchange properties resisted this trend. I'm very grateful for that too.
For one, if you want to see the later answers, you need to log-in. On SO you can just see everything, and it used to be that you could post a question as a guest.
In addition, there is a whole family of sites on StackExchange, each with their own set of active users and people. To me, Quora just seems like a better version of Yahoo answers, while SO is what I want a successful Q&A community to be.
In those same four years Facebook, Twitter and the likes of Quora have exploded, and made the Internet worse. Yet at the same time all the Stack Exchange properties resisted this trend. I'm very grateful for that too.