beat a dead horse
對已經解決了的問題或無法改變的情況再次花費時間或精力
口語·表示爭論或討論已無意義
英文釋義
to waste time or effort on something that is already finished or resolved
例句
Stop beating a dead horse; we already decided to cancel the event, so there's no point arguing.
典故來源
源自19世紀美國西部,指鞭打已死的馬毫無意義,比喻對已結束的事情浪費精力。