It is such a good (and short) video that I had to write something about it.
It starts by saying that the documentation for the Ecto library is great but, because it is a big library, and the documentation is super specific, it will not be so useful for new learners. New learners will have general questions, not specific ones.
Then the video makes an analogy: suppose you are visiting a city for the first time and someone gives you a phone book. Is it useful? Not much. A tour guide is much more useful. The analogy is that the documentation is the phone book, and the Programming Ecto book is the tour guide.
And this analogy (which I don’t know if it is new) is what I thought was great on this video. Everybody needs a tour guide when he/she is starting to learn something. That’s why I love technical books. In particular, I love PragProg books.