It's mind-blowing how much information Facebook knows about us. We voluntarily give that information away, but we don't often realize just what can be done with that info.
Giving away your information is way easier than you'd think. Have you liked or shared something on Facebook, ever? Then Facebook and other data companies are using that information to guess what you like and target you for ads.
Don't believe me? The University of Cambridge Psychometrics Centre has created a quick online quiz that will show you just how much advertisers and other data companies know about you.