Failure to encode can be explained by not engaging information in your life long-term due to lack of concentration or not paying attention to the information presented. As I think about this particular theory, I think of Leonard's photos. He has a photo of everything, from the sign of the motel he stays in to his car, to replace new memories. Decay theory is described as the process of losing memories that go unused and slowly leave our minds. Sometimes we fail to remember something because we haven't thought about it. This theory explains why we can't remember exactly how to do old high school math test problems years after we graduate. We don't practice these types of problems, so we can't remember them because they just disappear. We also have the theory of interference. This may be because we are not focused on something and our attention is divided. Retroactive interference can be explained as “with the old and with the new”. You are lost because you cannot remember the old password of your computer because the new password is the one you memorized forcefully. This lets you forget the old password in the process. There is an example of this type of interference found in the film when Leonard searches for a pen to try to concentrate on writing about his argument with Natalie, but he is