Every action on the left is trivial and ordinary — the kind of thing no one thinks twice about. Turn a few on and watch the dossier on the right fill with things you never said. The danger was never one data point. It’s the sum.
You didn’t tell anyone you were pregnant, broke, or where you work — yet the profile “knew.” That’s aggregation: dozens of meaningless crumbs (a purchase, a search, a time of day, a place your phone sits) combine, through correlation, into intimate guesses. This is real — a major retailer once inferred customers’ pregnancies from shopping shifts and mailed baby coupons, sometimes before the family knew. Two things make it dangerous: the inferences are invisible (you never see your own dossier), and they are often wrong — yet they’re still used to set your ads, your prices, your risk scores, even who sees your job posting.
A teaching model — the specific inferences are illustrative, but the mechanism (and the pregnancy example) are real. No accounts, no tracking, nothing leaves your device. Free to reuse (CC0).