I constantly see big ad pushes for things I have not been talking about, but is the sort of thing that other people may have been talking about.
Then people talk about things they have seen ad's and you talk to them about the ad and then you see an ad and you thing the phone has been listening to you to hear you talk about it, when infact the conversation came from someone else seeing the ad.
Your conversation is driven by the ad's, not the other way around.