The story
A piece of advice to prospective authors that they must kill their “darlings”, i.e. suppress overuse of their favorite expressions, tropes, characters, etc. Often attributed to William Faulkner (1897–1962), but already expressed earlier by Arthur Quiller-Couch (murder one's darlings); more recently popularized by Stephen King.
Etymology from Wiktionary, CC BY-SA 4.0.