Nicolas Malebranche

He has willed - He wills incessantly - that the modifications of the mind and those of the body shall be reciprocal. This is the conjunction and the natural dependence of the two parts of which we are constituted.

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.