Alternatively, I could have waited until someone noticed my advertisement to start to write the book or produce the product. Pull.
So where is push and where is pull better?
I see ads as purely a push based model; to the GP point, if it was worth looking for why wouldn't you already be looking for it via a pull based method. But you obviously don't know what you don't know. Either 100% push or 100% pull won't be optimal. This is where I see recommendations and being able to swap between a spectrum of XX% push and YY% pull algos is helpful.
For example physical music, i can walk into a record store and decide to buy a handful of records; the store owner can then see those records and recommend more that I could also enjoy and even ask me questions to make those more accurate. This isn't 100% push or pull and also has an element of human curation that inherently doesn't scale but is possibly the most effective approach. I can do the same thing online via discogs and get some automated recommendations. I have a choice between the two and depending if it's a genre I'm familiar with (human recommendation might give me something new) or a new one I'm trying to explore (most popular records recommended by discogs are a good starting point) i can choose one or the other.
I see solving this problem as a key one for the whole creator long-tail, 1k fans, etc... problem-space. Don't have the answers but those are some general ideas.