No two people ever remember an event in exactly the same way. Ten witnesses to the same automobile wreck will have many similarities in their accounts of the event, but there will also be glaring differences. The same is true for our memories of past events.
A good example is from a 10-year old girl who was involved in a minor sledding accident when she was three years old. She believes that she remembers the event, but her memories are based on what she has heard over the years as her family members recount the accident to others. The little girl's account goes something like this:
"When I was little, I was hit by a car while I was sledding down a hill in Colorado."
In actuality, the little girl was sledding down a slope too steep for her comfort, and she flipped over, scratching her face. As she flipped out of the sled, she bumped her face on the snow and some swelling occurred. Later, she heard her family members exaggerate that even though the accident was minor, she looked like she had been hit by a car.
The difference in these two versions of the story accentuates our need to only tell what really happened in actual events. It also reminds us that memories are fragile and changeable things. Now that the little girl has been told what really happened, her "memory" of the event has changed to include the truer version of the accident. However, her actual memory of the event is still based on what she has been told not on what she remembers.
If the girl's parents had not heard her telling the story in her original version, they may not have realized she was carrying around a "faulty" memory of an event. Since they did, however, they were able to "correct" parts of her story with new information. But how often do we get to adulthood and never realize that what we think we remember is not how an event played out at all?