Making up memories.

From The National Memory Test:

The brain is a genius in interior knowledge design, allowing us to tuck away even the most trivial of items for future reference – to the benefit of quiz junkies world over. But it can also bear false witness.
When we encode memory we add certain tags to it – information about how we felt at that time, or what time of day it was. In discussing the memory these tags can be added – and falsified. For example if a witness to a crime is questioned about the appearance of a women wearing a hat, they may add the hat to their memory of that person – even if it wasn't really there. They added that extra memory tag when the original memory was discussed.
Often early memories can seem very vivid, but are only images from a photograph or stories from family and friends that you store in your mind as a real memory. You can distinguish between the false and real memories by examining the emotions and sensory information you associate with the memory. Real memories should have tags about how you feel, and what was happening around you at the time.
Not only do we falsify memories, we also like to put a positive spin on them. Research on memory shows that the feelings associated with bad memories tends to become more positive with age.
We create silver-lined autobiographical accounts of our lives...

http://www.nationalmemorytest.net.au/retreivingmemories.aspx