Write what you like; there is no other rule.
By rights you're a king. If I was you, I'd call for a new deal.
A story with a moral appended is like the bill of a mosquito. It bores you, and then injects a stinging drop to irritate your conscience.
If you can't write a story that pleases yourself, you will never please the public. But in writing the story forget the public.
Inject a few raisins of conversation into the tasteless dough of existence.
In the Big City a man will disappear with the suddenness and completeness of the flame of a candle that is blown out.