In this chapter of, The Brain Rules, Medina speaks about how we forget everything very quickly. He speaks of the 4 stages of processing memories, they are: encoding, storing, retrieving, and forgetting. He mentions how the brain has a better chance of remembering something that you constantly repeat to yourself. When you try to remember something, the memories you have that were split into fragments, try to re-connect to make that memory again. I believe this is why retracing your steps works to remember something you forgot.