A gem is not polished without rubbing, nor a man perfected without trials. 前句套用 <<三字經>> : 玉不琢、不成器 後句套用俗語 : 不經一事、不長一智 或者 璞玉 不經 琢磨 無以 成 器用 庸夫 需經 錘鍊 始得 成 完人

don't mislead people, it's not 成语, it's 谚语

玉不琢不成器，人不学不知义。 It is from The Three-Character Primer, classic texts of ancient China. The literal meaning of the last part of this sentence in Chinese is that you don't know the truth without learning .

玉不琢不成器