“Kill your darlings” was an expression Sir Arthur Quiller-Couch came up with, to tell young writers not to fall in love with a particularly fine passage. He wrote,
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.’
It doesn’t mean “Kill all your characters”. Or even, “Don’t treat your characters with compassion and love.” Even when bad things happen to them, as they will.
And, for the record, when I write something I’m particularly pleased with, it stays.
Another thing that’s lost about this advice is that he was talking about style– not content, not characters.
The particular problem he was trying to address was trying to look smart by showing off a big vocabulary with flowery writing. More often than not, the person doing this doesn’t actually have the skill to pull it off, and they end up looking ridiculous.
Painfully baroque prose isn’t a temptation for most writers anymore. This advice was given in 1916, long before simple sentences became fashionable.
I’ve encountered this writing vice occasionally in literary writing workshops and magazines and academic journals, but it’s much more likely to show up in arguments on the internet when someone is trying to intimidate someone who disagrees with them instead of making an actual argument.
This is the whole paragraph from the book that contains the advice:
“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. 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.’”