Kill your darlings!
There seems to be an Anglo-American dispute over this quote, with some attributing it to the American novelist William Faulkner:
In writing, you must kill your darlings!
while others go for the older English writer Sir Arthur Quiller-Couch:
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.
Either way, it’s good advice. We all overwrite at times, and for writers of non-fiction, there’s an additional menace: the fascinating sidetrack. Continue reading