Last year I was dropping my daughter off at a friend's house. The friend's dad met me at the door and we chatted. It was the first time that we had ever talked about anything. Literally just met the guy. In our conversation, we mentioned an app that he just started using (and was in fact using when I pulled up). It's an app that I would never use since it was about Golf and I don't play or care about golf. Before I pulled out of his driveway I checked Facebook. I kid you not, an ad for that app was on my news feed. I'd never seen it before, ever. Somehow they correlated his installation of the app, with my account, and showed me something that there was a chance we discussed. Twilight Zone stuff, I tell you.