Memory is the record of experiences accumulated in the mind. It is the knowledge that guides learning and behavior. Every sensation we experience leave a momentary trace, or a sensory memory. If we pay attention to the sensation, it is held in our working (also known as short term) memory, which can hold 5 to 9 pieces or chunks of data at once. If information in our working memory is rehearsed (actively attending to), it can be encoded into long term memory. Issues of retrieving information from memory can arise at any stage in this process. If you do not pay attention or fail to rehearse a piece of information, it will never be encoded. You could also encode something into long-term memory and have that information replaced with new or old information.
There are also different kinds of memory. Implicit memories can take the form of procedural knowledge or conditioning. Explicit memories can take the form of generic memory (facts, information) and episodic memory (life events). Memory can be enhanced by creating visual images and by linking a memory to some emotion. It is also important to note that memories are not snap shots of life. When we encode memories, we integrate them with our own thoughts, experiences, and perspective. Memories can also be changed based on how we discuss them. If you and a friend discuss a shared memory and their account differs from your own, you may eventually integrate their story into your own story, and grow to think that this is your original recollection of the event.
Slumdog Millionaire(2008) demonstrates the power of emotion in enhancing memory. Jamal manages to make it all the way to the million dollar question on Who Wants to Be a Millionaire by recalling emotionally charged moments from his life that, by chance, relate to each of the questions. Unsurprisingly, all of these moments are tied to the love of his life--Latika. Love is certainly an emotion that is powerful enough to make the most obscure memories last.