No, You Haven't Forgotten Everything - Scott H Young

Much of what we learn is beyond our ability to recall later. For example, how well would you do at a final exam for a class you studied a decade ago?

However, learning something the second time round is much faster.

Early theories of forgetting were based on decay. They assumed unused memories weaken over time, much like unused muscles.

Another major factor in forgetting is Interference from other memories. The more memories we acquire, the more they become associated with familiar cues, making it harder to retrieve a particular memory. This is not a defect. It’s a feature. Memory is only useful if we retrieve the right memories at the right times and suppress all competing alternatives.