Grinding an Iron Pestle Down to a Needle

The other day I was listening to a ChinesPod podcast and they talked about the saying "铁杵磨成针" (tiě chǔ mó chéng zhēn) [lit. iron pestle grind into needle]. Then coincidentally I found an anecdote in my "Tales and Traditions, Vol. 1", which is kind of curious and funny. I'm going to leave you the story...