恨ㄏㄣˋhèn鐵ㄊㄧㄝˇtiě不ㄅㄨˋbù成ㄔㄥˊchéng鋼ㄍㄤgāng

  1. 憾恨鐵煉不成鋼。指對期望的人不成器，感到焦急不滿，而有所責求、惋惜之意。《紅樓夢·第九六回》：「只為寶玉不上進，所以時常恨他，也不過是恨鐵不成鋼的意思。」

英lit. to hate iron for not becoming steel, to feel resentful towards sb for failing to meet expectations and impatient to see improvement (idiom)​