In the middle of the night, I came up with a solution to a problem I've been working on, but didn't want to sit up to write it down because I was sure I would remember it.
I don't.
I did that.
My notes were so cryptic, I could only figure out what they were saying in retrospect.
I was trying to write a SciFi story, and needed to kill one of two characters in the prologue. Figured out which one in the middle of the night, wrote down 'blond', and went back to sleep.
Neither of the characters were blond.
After getting a ways in, I realized I had killed the wrong character, and set that story aside.
Months later, I realized that 'blond' was a reference to Joffrey, and that I needed to kill the character that could allow an illegitimate heir to take the throne.
I have a client that records a voice memo and then goes back to sleep and forgets what they dreamed.
When we talk about their dreams we are both listening to it for the first time.