You know how someone does an amazing trick, and then they show you how, and you say, "Oh, I see, that was easy once you know the trick." Well, that is not the case with this art, at least for me.
One problem with art books is they will have some exercise to draw a face, and step one will be an oval and step two will be a few more ovals, and I am following along well, and then step three the whole face is suddenly drawn in where the ovals were. Art books all do this and it drives me crazy. Well, at least the guy in the linked video shows every single little step. And it still seems a miracle that the picture emerges.