I have heard the theory that every time we remember something it is influenced by our thoughts, feelings, and beliefs at the time of remembering. That implies that the memories we think most about are the ones that have been most distorted from their original form.
An exaggerated version is in effect for stories recounted to others. They always need to be selective in detail to make the account manageable in length, and simple tweaks to make it more comprehensible and straightforward have a tendency to persist in later retellings. In particular, I find in myself a tendency to combine the most memorable features of multiple events into a single recollection/story — not, for example, as two or more different parties at distinct semi-remembered places, but one party which sets up a subsequent part of the story.
I suppose the phenomenon demonstrates the value of contemporaneous records and accounts like journaling. Doubtless our interpretations of those records are influenced by subsequent context, but at least the record itself is immutable.
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