To be clear, OP is not questioning the validity either. You are, and that’s a separate discussion.

If I tell you “playing with fire is risky”, and then you bring up an old book to me where is it written “playing with fire is risky”, the discussion is not about whether I told you that from the book. It is not about whether my advice is valid or the book is valid. The discussion is just that people who had read the book should have already known “playing with fire is risky”.