Lynch says it is not known exactly how this happens. There is evidence that new memories can partially override old ones, so seeing a white house similar to Grandma's yellow one might unconsciously tint the original memory. It is also known that newly formed memories are, like unset concrete, vulnerable for a few hours. During that time, the brain can send a code that erases the new memory. All this is more important than most people realize, Lynch says.
Most people think of memory only as remembering to pick up milk on the way home.
In reality, you use memory constantly. You leave work and recognize your car among the hundreds in the parking lot. You remember how to open the door, how to start the engine, how to drive home. You hear a song on the radio and remember the emotions you felt when you first heard it. You see a red light and unconsciously remember that you're supposed to stop.