Many people strive to remember parts of books, most probably because they assume that the content of a book is useful only if we are able to carry it in our minds. But what is, really, the usefulness of remembering? Imagine that you are a computer which has stored whole books in it, and you can reproduce any part of them at will. What's the point of that? I don't think there is one, that is, unless you want to show off. Otherwise, remembering is not any more useful than opening the book, or Google, at any time and starting to read.
What's the usefulness and impact of books then? Why do we read them? One reason is just pure entertainment, i.e., some kind of ephemeral joy. That is, we just have fun, we arouse our emotions etc. This is especially true for fiction, but even non-fiction. Sometimes you just want to read some well-crafted sentences and coherent arguments instead of diving deep into a story 1.
The other reason is for the books to affect us in some way. When I say affect, I mean to change us, to modify our behavior, to influence our actions, in general, to shape the way we think. When this happens, the content passes from the book to our mind, to our conscience and consciousness. From then on, we do carry the content with us, but it is quite different from “remembering”. I understand the latter to mean that we store, and maybe reproduce, the original content as much as possible intact. And it is precisely why in this case, the content has not become part of us, but is rather, figuratively speaking, across us — we treat it and carry it like any other object, similar to how our keys feel to us 2. In contrast, when a book affects us, we incorporate its ideas, we embrace them, they become part of us. And in doing so, they change shape — they get molded, adapted, interpreted so as to get incorporated into our knowledge, belief and value systems that make up who we are. And then, the original content is almost indistinguishable from the rest of us, because it is now part of us. Over time, and the more we read, we, or others, can discern differences compared to our past self, but we cannot pinpoint the “new parts”. This is because the way we think is closer to an alloy, whose constituents are indiscernible, than a mosaic, composed of separate, identifiable parts.
Strikingly, this is the reason we cannot completely decide which books we will “carry” with us — that is, which books will affect us. We can only partly influence that by choosing which books to read. But which of those books will actually have an impact on us is determined by a complex system of beliefs, values, aesthetics and opinions, shared by us and the author. Books that we think will change us can be proved quite indifferent, and books that seem really boring and trite end up challenging some of our deepest-held beliefs 3. So, you may want the reading of — enter pop title like To Kill a Mockingbird, The Apology of Socrates, Genealogy of Morals etc. 4 — to be proved a life-altering experience that stretches your horizons irreversibly — and you may want that so that you can sound cool at parties — but when you actually read it, you may have to accept that, at least for you, this book is boring and devoid of depth and/or taste. That's life... Now you will have to talk about how “Logic and Structure is pretty underrated”. And nobody will want to hang around you.
Furthermore, because the impact of books is not based exclusively on the content, but mainly on people's (subjective) interpretation of the content, the content itself, which created these interpretations, becomes less important than them! To quote Walter Lippman 5:
Marxism is not necessarily what Karl Marx wrote in Das Kapital, but whatever it is that all the warring sects believe, who claim to be the faithful. From the gospels you cannot deduce the history of Christianity, nor from the Constitution the political history of America. It is Das Kapital as conceived, the gospels as preached and the preachment as understood, the Constitution as interpreted and administered, to which you have to go.
We should be able to deduce some obvious repercussions of this phenomenon. A negative one makes an appearance when the original content is grossly misinterpreted and stretched out of proportions to the point that there is little relation to the original conception. Or, when we commit the error of presentism in our interpretations, when we do not understand the context and subtext, or simply when we blatantly close our eyes to the facts.
However, there is the other side of the coin, that of the positive interpretation, possibly towards new intellectual avenues, which has accompanied a great part of scientific progress. That said, having had some experience with the academic world, a common occurrence is when a paper's descendants introduce more powerful ideas than the paper itself. Then, falsely, sometimes we think that the value of these descendants must have been created by this “first paper”, even though the descendants might have deviated so much from the original, they may be so novel and creative, that a sober observer would only talk about “motivation” or, at best, “inspiration”.