Question

Why does the ghost undermine the narrator's faith in his ability to write ghost stories?

Answer 1

The ghost undermines the narrator's faith in his ability to write ghost stories by disclosing the truth that it is not the narrator himself but the ghost who help him write ghost stories which the narrator was overconfident of.

Answer 2

After writing a few successful ghost stories, narrator felt over confident about his ability so but Helen, the ghost, undermined his faith by revealing him that she gave her ideas to write..