In classical Greek myth, the gods could not undo what another god had done. When Hera blinded Tiresias, Zeus couldn’t just simply say “nuh-uh” – only Hera could (and eventually did) give Tiresias back his sight. Zeus could only do something to compensate for what Hera had done; in this case, he gave Tiresias metaphorical sight, in the form of the gift of prophecy.
Storytelling in the Three Moons works the same way: if a player introduces a detail to the story, only they can undo it later. To put things in improvisational theater terms, there is no “no”, “no, and” or “no, but” here. There is only “yes, but” or “yes, and”.
Try the rule out in practice and let me know how it goes!