Personal story time. A few years back, I texted (through Whatsapp) a colleague for a few minutes about a friend taking up welding as a supplementary source of income, and immediately (within the day) received a targeted ad in the Duolingo app for... welding torches. Important facts, I don't weld, I've never done any welding and I don't know anything about welding. How this bit of info got from whatsapp to whomever was providing interstitial ads in the duolingo app, I have no idea. My best guess is still that google's keyboard app is logging every single keystroke I type and aggregating it in a database somewhere. I can't fathom how that shit isn't extremely illegal.