L'esprit de l'escalier

L'esprit de l'escalier is a French term, used in English, for thinking of the perfect reply too late. The name comes from Denis Diderot's description in his "Paradoxe sur le comédien" of being left speechless during a dinner at the home of statesman Jacques Necker, because a sensitive man "doesn't come to himself again until at the bottom of the stairs." The stairs refer to mansion architecture, where reception rooms sat one floor up, so reaching the bottom means having left the gathering. Equivalents exist in Yiddish, German, Russian and Chinese.