TikTok has stepped over the point between the familiar self-directed feed and experience based on algorithmic observation and inference. When you open the app, you don't see a feed of your friends, but a page called "For You" - It's an algorithmic feed based on videos you've interacted with or just watched.

It's not full of people you know or things you've explicitly told it you want to see. It is constantly learning from you and builds up a model of what you tend to watch. In short, it is like an Instagram centered entirely around its "Explore" tab.

TikTok is reportedly 500 million users strong. It’s been a while since a new social app got big enough to make nonusers feel they’re missing out from an experience.

TikTok is an app for making and sharing short videos. For the Americans, it is one of the most popular of many short...