Meaning "to grind an iron pestle into a needle"; an idiom used to describe how anything can be accomplished if one works hard and stays persistent. It refers to a story where the famous poet [[李白|李白|li3 bai2]] was inspired to continue his studies after seeing an old woman trying to grind a thick iron bar into a sewing needle.

literal meaning: if you work at it hard enough, you can grind an iron bar into a needle; used to say that with perseverance and effort, any difficult task can be accomplished.