> I'd assume based on personal experience that higher retention rates occur in subjects the reader is already familiar with. In that case only a fraction of th

> I'd assume based on personal experience that higher retention rates occur in subjects the reader is already familiar with. In that case only a fraction of the information in the book can really be learned. Yes, you can read a book you already know very well and retain 95% of the information, but then what's the point of even citing any numbers? > If you're reading into a subject you're not familiar with and rely on "your brain" to optimize what's most relevant for that subject I'd bet you'd come out looking like the stereotypical "know it all" in any related conversation. Only if you think you retain 90% of what you read.