The story of the iron pestle grinding into a needle

Mozhenxi is at the foot of Xianger Mountain in Meizhou. According to legend, Li Taibai studied in the mountains, but he gave up and left before he finished reading. After crossing the stream, I saw an old woman grinding an iron pestle. Li Bai was surprised and asked her: The old woman replied, "I want to make needles." Li Taibai asked, "Can you grind the iron pestle into a needle?" The old woman replied, "Just do it well!" Li Bai was moved by her perseverance (will) and returned to the mountain to finish her studies. The old woman herself said that her surname was Wu, and now there is Wushiyan beside Mozhen River.

Extended data:

On the surface, this idiom is positive. But if you think about it carefully, isn't it an obvious waste to grind the iron pestle into an embroidery needle? It's a waste of iron pestle and precious time, not to mention an old lady? Persistence is valuable and important. But we should also pay attention to an "efficiency".

References:

As long as the kung fu is deep, the iron pestle is ground into a needle _ Baidu Encyclopedia