磨杵成針

mo2 chu3 cheng2 zhen1

to grind an iron bar down to a fine needle (idiom); fig. to persevere in a difficult task, to study diligently

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磨杵成針|磨杵成针 [mó chǔ chéng zhēn] ► to grind an iron bar down to a fine needle (idiom); fig. to persevere in a difficult task ► to study diligently