Here someone might object,
"Then you didn't really remember it,
you only thought you did!"
This person is using "remember" in the "strong" sense,
in which remembering involves not only "having a feeling of recollection"
but also that the event about which you have this feeling really did occur.
If it didn't really occur, then "you don't really remember it, you only think you did." In this sense, it is a defining characteristic of (really) remembering that the event actually occurred; therefore, in this sense it is logically impossible to remember something that never happened