I finally reached chapter 5 (at my own slow path) and now I understand John's statement:
> as the book proceeds and the 'sketches' get more sketchy, leaving me to fill in more details.

And that's why I will miss your lectures for chapters 5 - 7 so much!
> I don't know if I should be filling in so many details

Without your extra details and rationale explanations, I sometimes get sooo confused... even if the book is already super pedagogical.