只要功夫深，铁杵磨成针

proverb

if you work at it hard enough, you can grind an iron rod into a needle; with perseverance and hard work, any difficult task can be accomplished

This proverb originates from the story of the Tang Dynasty poet Li Bai, who was inspired by an old woman grinding an iron pestle into a needle. It is used to encourage persistence and diligence.