The most important, the longest lasting, the strongest emotional, and the most practiced memories are the ones that are embedded the deepest in the brain, and because we have retrieved them so many times previously, they are the most able to be retrieved. We all hear about people who can remember their youth, their phone number, or street address from 70 years ago, but they cannot recall what they had for breakfast. The memory of this morning's breakfast wasn't rehearsed, and wasn't very important, so it fades away quickly.
Daniel Levitin