Our eyes are very good decievers, and we are very biased as to what we can convince ourselves to have seen.

Sometimes, people can even fill in gaps of a story with something that seems right, or something that other people keep repeating to them.

Eye witness testimony is not entirely reliable. You guys ever hear about an experiment where people were told to pick someone out of a line-up? They chose one that they were SURE was the perp- except that as a test, the real perp wasn't even in the line-up!