We know that people make up false memories
if prompted. But since our brain never stops being a jerk, we can also
convert real memories into things we believe we imagined.
Cryptomnesia
can strike via our own memories, or our memories of things that others
tell us. One of the most famous cases of cryptomnesia destroyed the
fantasy-writing career of Helen Keller....
http://io9.com/cryptomnesia