21:00: what are the other 6 books that he had to write? It would be awesome if he (Michael W. Lucas) could list recommendations for other books to read, below the description or something, so people know how books are correlated. If people want to read it without reading the other books ok, but for those who don't know how they correlate (i.e. me 😅). it would be nice if I can read through them in order, so you don't get frustrated not knowing what is getting discussed and have to stop to reading and read another whole book to grasp the concept.