The natural human genius for creating patterns gangs aft agley.
A common example of this is when two people -- call them A and B -- have an argument on a certain topic -- call it X -- which is not resolved to their satisfaction. When the topic arises again later (as it always seems to do), should a third person -- say, C -- say something that reminds Person B of something Person A once said, Person B picks up the earlier argument where he left off, placing Person C in the role of Person A and assigning to Person C all of what Person B believes Person A believes. Person B, in this case, notices a similarity and completes a pattern that isn't necessarily correct.
It can be a bit disconcerting to play the role of Person C in such a situation, especially if you wouldn't know Person A from Adam or A's and B's earlier argument from the Lincoln-Douglas debates, but it's usually easy enough to notice when Person B is arguing at someone else but with you.