The subconscient records everything, and if you have the impression that an ordinary book leaves no effect, it means that you are not conscious of what goes on within you. Each time you read a book in which the consciousness is very low, it strengthens your subconscient and inconscient—it prevents your consciousness from rising upward. It is as if you threw buckets of dirty water on the efforts you had made to purify your subconscient.
Ref: Questions and Answers 1950 – 1951