question: Why do some memories stay with you forever and some you forgot? Also how can you forgot a memory for a long time and then suddenly remember it again?
comment: Memories are basically just pathways in our brains. The more you recall something, the stronger related pathways become. Likewise, if a pathway goes untriggered, it becomes weaker but doesn't disappear. Its part of why recalled memories can be twisted or overwritten. And makes wilfully forgetting something such a mess. The act of recall just reinforces that connection.
passages: Section::::Pathways of recall.
  
  Memories can be very different in nature and as a result, different memories are stored and subsequently recalled via appropriate neural circuitry in the brain. The pathways of recalling a memory will therefore depend on the nature of the remembered stimuli that is being retrieved. Memory representation of different types of information can take on various forms.
  
  Section::::Pathways of recall.:Language recall.
   Section::::Aging.
   Section::::Depth of processing.
  
  Craik and Lockhart proposed a framework for the various levels of processing a stimulus. They assumed that the level or depth of processing of a stimulus has a large effect on its memorability. Deeper analysis produces more elaborate, longer-lasting and stronger memory traces. The stronger memories are, the more likely they will be to exhibit recovery.
  
  Section::::Depth of processing.:Reminiscence.
   For example, if someone tries and fails to recollect the memories he had about a vacation he went on, and someone mentions the fact that he hired a classic car during this vacation, this may make him remember all sorts of things from that trip, such as what he ate there, where he went and what books he read.
  
  Section::::Cues.
  
  Section::::Cues.:Semantic cues.
   Section::::Theories.:Spatiotopic fusion hypothesis.
   When a memory is formed, cues associated with the formed memory form a constellation of nerve networks in which the memory is stored. While the cues are present, the nerves that form the constellation are active and the memory is being worked on in short term memory. When the cues are no longer present, the constellation is no longer active and is waiting in long term memory storage for when the cues are once again present.
   Emotional experiences and events are somewhat fragile and take a while to be completely set into memory. This slow process, referred to as consolidation, allows emotions to influence the way the memory is stored.
   When experiencing an event for the first time, a link is formed in the hippocampus allowing us to recall that event in the future. Separate links are also made for features related to that event. For example, when you meet someone new, a unique link is created for them. More links are then connected to that person's link so you can remember what colour their shirt was, what the weather was like when you met them, etc. Specific episodes are made easier to remember and recall by repeatedly exposing oneself to them (which strengthens the links in the memory space) allowing for faster retrieval when remembering.
   Section::::In popular culture.
  
  Memory phenomena are rich sources of storylines and novel situations in popular media. Two phenomena that appear regularly are total recall abilities and amnesia.
  
  Section::::In popular culture.:Total recall.
   Section::::Environmental.:Environmental reinstatement effect.:Short-term reinstatement effects.
  
  Momentary forgetting, such as forgetting what you wanted to get from the kitchen after getting up from your desk, is frequently experienced in day-to-day life. Usually what was forgotten can be remembered again by returning to the context where the event began. For example, imagine sitting at your desk and deciding you want to get a drink from the kitchen. Once you get to the kitchen, you completely forget what you wanted there. If you return to your desk, you will most likely remember what you wanted from the kitchen.
   Topographic memory involves the ability to orient oneself in space, to recognize and follow an itinerary, or to recognize familiar places. Getting lost when traveling alone is an example of the failure of topographic memory.
  
  Flashbulb memories are clear episodic memories of unique and highly emotional events. People remembering where they were or what they were doing when they first heard the news of President Kennedy's assassination, the Sydney Siege or of 9/11 are examples of flashbulb memories.
  
  Anderson (1976) divides long-term memory into "declarative (explicit)" and "procedural (implicit)" memories.
  
  Section::::Types.:By information type.:Declarative.
   Section::::Phenomena.:Focal retrograde amnesia.
   Section::::Depth of processing.:Hypermnesia.
  
  Hypermnesia is an improvement in memory that occurs with related attempts to retrieve previously encoded material. Hypermnesia is the net result of reminiscence and forgetting, such that the amount of reminiscence must exceed the amount of forgetting resulting in a net improvement overall. Ballard was the first to observe hypermnesia using a multiple recall task in 1913, the same task with which he discovered reminiscence. After asking young school children to memorize poetry, he initially retested their recall abilities 2 days later only to discover that the class improved by 10 percent over the initial recall level.
   Section::::Spreading activation.
  
  In the brain, memory stores information in a network of nodes that are linked together. When a memory is retrieved, activation spreads on the links until it intersects or enough time has passed. If there is one association, the activation only has to spread to a single link whereas multiple associations would divide the activation to many links. Because there are so many connections, it causes the brain to take a longer time to identify the concepts and retrieve the memory.
  
  Section::::Plausible theories.
   "Second experience: "I visit a supermarket and go down the aisles. I see an unexceptional woman with a trolley. Three aisles further on, I see her again. I have not tried to remember her, but I have seen her and I can recognise her again a little later.""
   The remember-know paradigm began its journey in 1985 from the mind of Endel Tulving. He suggested that there are only two ways in which an individual can access their past. For instance, we can recall what we did last night by simply traveling back in time through memory and episodically imagining what we did (remember) or we can know something about our past such as a phone number, but have no specific memory of where the specific memory came from (know). Recollection is based on the episodic memory system, and familiarity is based on the semantic memory system. Tulving argued that the remember-know paradigm could be applied to all aspects of recollection.
   Section::::Mechanisms that link memories across time.
   Section::::Episodic memory.:Episodic.
   Section::::Phenomena.:Tip-of-the-tongue.
  
  "Main page: Tip of the tongue"
  
  A tip of the tongue (TOT) state refers to the perception of a large gap between the identification or knowledge of a specific subject and being able to recall descriptors or names involving said subject. This phenomenon is also referred to as 'presque vu', a French term meaning "almost seen". There are two prevalent perspectives of TOT states: the psycholinguistic perspective and the metacognitive perspective.
   Section::::Factors affecting retrospective memory.:Disease.:Korsakoff's syndrome.
   The Argentinean author, Jorge Luis Borges wrote the short story "Funes the Memorious" in 1944. It depicts the life of Ireneo Funes, a fictional character who falls off his horse and experiences a head injury. After this accident, Funes has total recall abilities. He is said to recall an entire day with no mistakes, but this feat of recall takes him an entire day to accomplish. It is said that Borges was ahead of his time in his description of memory processes in this story, as it was not until the 1950s and research on the patient HM that some of what the author describes began to be understood. A more recent instance of total recall in literature is found in 
   Section::::Causes.:Neurological causes.
  
  Section::::Causes.:Neurological causes.:Neurological basis of false recognition.
   Memory erasure is portrayed in "Eternal Sunshine of the Spotless Mind" (2004) and in the "Men in Black" movies. "Men in Black" features a device to erase the potentially harmful memories of extraterrestrial interactions in members of the general public. "Eternal Sunshine of the Spotless Mind" describes a process that targets and erases memories of interpersonal relationships the patients would rather forget so that they are no longer able to recall the experience. In "Paycheck" (2003) and "Total Recall" (1990) memory suppression is used to control and the characters are able to overcome the attempts and recall pieces of their memory.
   Section::::Social consequences.
   One implication of the encoding specificity principle is that forgetting may be caused by the lack of appropriate retrieval cues, as opposed to decay of a memory trace over time or interference from other memories. Another implication is that there is more information stored in memory relative to what can be retrieved at any given point (i.e., availability vs. accessibility).
  
  Section::::Amnesia and consciousness.
  