早知今日何必當初 [ㄗㄠˇ ㄓ ㄐㄧㄣ ㄖˋ ㄏㄜˋ ㄅㄧˋ ㄉㄤ ㄔㄨ; zao3 zhi1 jin1 ri4 he4 bi4 dang1 chu1] if I (you, she, he...) had known it would come to this, I (you, she, he...) would not have acted thus (idiom) to regret vainly one's past behaviour ◄ ►