Characters Suddenly Appear: If fully-formed characters that a novelist doesn’t know, suddenly appear, does the novelist have a memory gap for creating them? Yes.

Sally Rooney video interview. https://www.youtube.com/watch?v=iIGSMGdgCyQ

[Added Sept. 28: She says that the characters just walked into her brain fully formed. She does not know where they came from. But since they could not have been created by anyone but her, they must have been created by a part of her mind of which she is not aware: a conscious, creative, story-telling, alternate personality. However, neither the author nor the interviewer reason this out.]