Choosing Books for Autodidacts
This is the place to start learning a subject from scratch, that is already being taught at schools as a basic knowledge every human should have. School textbooks are vital whatever your motives are:
Necessity, curiosity, nostalgia, familiarity, or "any" pleasure one has during studying, not necessarily related to the subject learned, boosts learning MOTIVATION.
You need them to further your knowledge of a particular subject you want to be professional at, either because you love it, want to teach others about it, or want to promote your career with it. You may need to take an exam too, to prove your eligibility for the job, to yourself and others.
Simplified vs. Professional
Abridged, illustrated or popularized books; books for children, beginners, dummies, etc. are especially useful when the subject is difficult:
Not all books are worth reading. Like humans, some are talkative, awkward, dumb, shallow and useless, whose fate is being forgotten and thrown out, down the abyss of history. This doesn't compare to the deep pleasure, solacing company and "valuable" knowledge found within the pages of a good book. Like good food, it needs careful selection and preparation first, preparing the body and the mind.
Good books involve the reader; they are not just convincing or informative. A book is not worth reading if it's not life-changing. No one can fully understand a subject they can't relate to and learn in practice. A well-educated person knows that real knowledge is incomplete unless it's fully tested and empirical. However, since we have no time to have all the experiences books are written about, let alone no wish to do so if they were bad experiences, we'd better choose books that exhaust all possibilities, putting the reader in the characters' shoes in fiction, and allowing argument with the author in non-fiction.
An assignment, a lecture, a book, a story ... won't suffice if there's no involvement. There are already some attempts of interactive books, where the reader is left to write their own parts based on a series of choices. On the other hand, simulators, sophisticated video games and other forms of virtual reality are quite involving, although many are still more about excitement than teaching. A perfect future prototype would be an interactive book that includes the richness of ideas, that most lectures and assignments lack, in a personally involving way, that lectures and assignments have. Eventually, it will be a book, not human, that does the act of teaching (when human teachers become obsolete), with the main goal of fully transferring data from a book into a someone's brain. Hopefully, in the future, brain chips and transplants will make this task much easier. Until then, our primary source of knowledge is well-written all-encompassing books.