I can forget about books with no problem. Sometimes after being 3/4 through a story a small feeling sets in that you somehow know the content and then you read

I can forget about books with no problem. Sometimes after being 3/4 through a story a small feeling sets in that you somehow know the content and then you read something that makes it clear you already read it. It isn't even a sign of quality, happens with interesting and boring books. Perhaps it is different with nonfiction but I doubt it. Certainly didn't work with my french textbook. What I think you cannot unlearn is some motor skills like cycling or skiing. Learned skiing at the age of 4-6 and then never came to it for nearly 15 years. Was afraid I would have to relearn everything but it was absolutely no problem as if I never did anything else the last decade. Maybe age of learning is a huge factor here.