Forgetting, which seems to be a memory failure, is in fact a routine knowledge maintenance procedure. We mainly forget information either because it has not been used for a long period of time or because some information seems to contradict with newly attained information, hence the old information needs to be overwritten with the newer one. Ever wondered, why do you forget where you put the keys to your apartment whereas you still remember how to drive a car, although you learnt it years ago? An important concept here is the distinction between explicit and implicit memory.