Information in the sensory memory disappears in approximately one second. For sensory information to last you must quickly move it to short term memory. Short term memory can hold a fact as long as you're thinking about it. Usually we can not store more than nine numbers in our short term memory. Information moves from short term memory to long term memory when it is rehearsed or practiced over and over again.
Intense emotion is another thing that helps put information into long term memory.
For example, a car crash experience may be remembered forever. Interference is when earlier or previously learned information hampers the learning of new information. For example, when a friend gets a new telephone number their old phone number interferes with the learning of the new number. Retrieval failure is when something you remember can not be retrieved. For example, this is when you feel like the word is on the tip of your tongue, but you can not think of it to say it.