Cryptomnesia
Also known as Inadvertent plagiarism
A forgotten memory comes back to mind without feeling like a memory, so you mistake it for a new idea of your own. It is a form of misattribution of memory and can lead to accidental copying.
In everyday life
In a meeting you proudly pitch a 'fresh' slogan, and a colleague points out it is almost word for word the one she suggested last month.
While drafting a wedding toast, a perfect line pops into your head, and weeks later you hear it word for word in a movie you loved years ago.
Why your mind does this
Memory is rebuilt each time we recall it, which lets us update what we know with new information. Revisiting a memory also strengthens it, so the things we return to often become the easiest to reach. This keeps our knowledge current without storing every version of every event.
Its family, in 30 seconds: Edited memories
How to spot it
Be suspicious when a brand new idea arrives fully formed and feels oddly familiar.
How to counter it
Before claiming an idea as yours, search your notes, email and the web for similar wording.
Same family: Edited memories
SourcesBrown & Murphy (1989)·Wikipedia