Mark Zuckerberg

Though builders may build, in the main they follow the plans of architects. Teachers teach, but they must have a text. Politicians govern, but only upon the flow of commentary that raises them up or casts them down.

Every time you log in to Facebook, every time you click on your News Feed, every time you Like a photo, every time you send anything via Messenger, you add another data point to the galaxy they already have regarding you and your behavior.