“There is a difference,” she said, “between immediate recall of facts and an ability to recall a gestalt of knowledge. We can’t retrieve the specifics, but to adapt a phrase of William James’s, there is a wraith of memory. The information you get from a book is stored in networks. We have an extraordinary capacity for storage, and much more is there than you realize. It is in some way working on you even though you aren’t thinking about it.”
IMO, this quote demonstrates a phenomenon I've long suspected to hold with the books that I read. The essence of a book's or an article's content is captured by a few key ideas and phrases (e.g., 'gestalt of knowledge', 'wraith of memory' in this case), but merely knowing these phrases is not enough. You need to read the entire book to have a sensation of the ideas getting fleshed out. The article on 'metrosexuals', the pamphlet on "the third estate", and the book on 'positioning' are other examples I can think of where this phenomenon plays out.
A rich 3-dimensional idea in the author's mind gets transformed into words. The words themselves are just information. You then fight with the words to reconstruct the idea with all its original potency in your mind. It is not necessary for you to recall every little detail of it unless you are an academic or specialist in the field.