The first principle theory is this: Any memory has two strengths, a storage strength and a retrieval strength. Storage strength is just that, a measure of how well learned something is. It builds up steadily with studying, and more sharply with use. The multiplication table is a good example. It’s drilled into our heads in grade school, and we use it continually throughout life, in a wide variety of situations, from balancing the bank account to calculating tips to helping our fourth grader with homework. Its storage strength is enormous.
