How often have you caught yourself on the wrong foot trying to place the person who has stopped to greet you while shopping at the city mall? The face seems familiar but try as you might but you just cannot recall his name.  Or, take the case when you parked your car only a short while ago and now you don’t really remember where to locate it.  The reason for the blank out of memory is that the brain, like the rest of the body tires out due to various factors such as exertion, tiredness etc.