You need the line that deflates a revenge quest: exposing the hero's crusade as a private ledger dressed up as justice, and forcing the recognition that the avenger and the monster are the same species.

Olivia Presteign strips Foyle's revenge of its nobility in one question: it isn't justice, it's bookkeeping against misfortune. She and Foyle are "a pair of monsters" because both built identities out of being wronged and then collected the debt from the whole world. Bester's verdict on the revenge engine: it never balances anything; it just converts private bad luck into public carnage.