"But I'd guess that most examples of this are selection bias; " Yup, that and most people's basic interactions are pretty easy to predict. You keep saving pictures of dogs labelled "me and fluffy down the park", do a few searches for the relative merits of dog food, send a few emails and texts about your dog, post some pictures up on facebook, IG, snapywhatever. Somewhere an algo has marked you as a dog owner. You'll get some dog food ads. Do a search for holidays and you'll get adverts for kennels. Humans think they're special and unique, but they are easy to predict at mass levels. You don't even need to be that accurate, the population is large enough that million to one chance occurrences will happen a few hundred times a day.