I remember the joy of clarity when I first reaised that magazines and television are a major example of this. The product they sell to advertisers is “eyeballs,” mine. I was deluded to think that by buying a magazine I had made a choice and paid for it; n fact I had barely paid for the paper it was printed on.
Credit is not mine for figuring this out. I think I got it from Newt Minow, the television critic, when I was a child.