Origins
Most writers know the phrase “murder your darlings” or “kill your darlings” that advises deleting what Sir Arthur Quiller-Couch called extraneous ornamentation.
Deliberate or not, such self-indulgent writing draws attention to sentence-level mechanics or clever observation, but it often does little to strengthen a story or further an argument.
The meaning of this phrase has expanded in popular culture to include killing off darling characters.
To begin with, let me plead that you have been told of one or two things which Style is not; which have little or nothing to do with Style, though sometimes vulgarly mistaken for it. Style, for example, is not—can never be—extraneous Ornament. You remember, may be, the Persian lover whom I quoted to you out of Newman: how to convey his passion he sought a professional letter-writer and purchased a vocabulary charged with ornament, wherewith to attract the fair one as with a basket of jewels. Well, in this extraneous, professional, purchased ornamentation, you have something which Style is not: and if you here require a practical rule of me, I will present you with this: ‘Whenever you feel an impulse to perpetrate a piece of exceptionally fine writing, obey it —whole-heartedly—and delete it before sending your manuscript to press. Murder your darlings.‘
– Sir Arthur Quiller-Couch, M.A.
from:
On the Art of Writing
Lectures Delivered in the University of Cambridge 1913-1914
Lecture XII, On Style, Wednesday, January 28, 1914
Full text is available from Project Gutenberg: