[gmerc]

In many cases it’s more than simple:

You had the conversation with someone and that someone googled/shopped/amaozned/clicked it. Or did before already, you don’t initiate every conversation in your life after all.

Now go and try getting a denial that they are not using the fact that you share a wifi with someone as parts of the recipe for the recommendation cake.

[red_admiral]

The arrow of causality can also go the other way. X corp is currently running a campaign targeting your area/demographic. A friend of yours sees and X ad and mentions something X-related to you in a private conversation. The next day, you see an X ad too.