True. I originally jumped in to object to the original poster’s idea that trying to control retention is pointless or impossible. There are too many variables t

True. I originally jumped in to object to the original poster’s idea that trying to control retention is pointless or impossible. There are too many variables that go into how much is objectively retained and for how long, especially since not every subject, author or title is read for the same purpose so success varies. I would, though, assume Bill Gates could retain 90% of a given book with less context than most people would need, i.e. retain a higher volume of new information than most people. That would be true whether measuring retention of everything in the book or just the new parts.