I was totally skeptical when I first heard stories about people's feeds being curated to suit what they were talking about in front of their computers, but then a couple of things made me rethink my views.
I was in the car with my friend once (both our phones were in the car with us too), and we were driving and it started raining. His wiper blades were shoddy and doing a bad job of clearing his windscreen. We had a 5 minute discussion on cleaning blades, where was the best place to get a replacement, etc. Neither of us picked up our phones, or did a search on 'wiper blades', nor asked Siri etc. about nearest places to buy.
But the next day, for the first time ever, I started seeing ads for wiper blades on my feed. They disappeared after a few days, but it was spooky, as it was for an item that I have never ever discussed, or seen on my feed before, or since.
Another anecdote. I was sitting working in my office the other day, when my son came in to talk to me about something. While chatting, he picked up a bass guitar that sits behind my desk and started playing the riff from 'Seinfeld'. I may have said something like "Oh, the Seinfeld theme - you know that was played on a synth and not an actual bass guitar?". Our conversation though, was about something else altogether.
A day later, on my feed, I see an ad about "How they played the Seinfeld theme" [0]. A totally specific ad like that, within 24 hours, totally unrelated to any searched I had done in my past. This one too disappeared within a couple of days.
[0] - https://twitter.com/dsabar/status/924763005014831104