Mom asks Daniel a simple question. Does he think someone at YouTube watches videos all day and decides what to recommend to him?

He thinks about it. Then says no -- that would be millions of people. So it must be some kind of computer thing.

He is right. And that computer thing has a name. It is called machine learning. And once you understand what it is, you start seeing it everywhere.

Here is the core idea. In many traditional programs, a developer writes explicit rules. If someone searches for this, show that. Very direct. Very specific. But some tasks are too complicated for that approach -- like figuring out what any individual person wants to watch next, across billions of people and billions of videos. So machine learning takes a different approach. Instead of writing every rule by hand, you give the system large amounts  ...