Great writing always comes from endless polishing.
Tips
history
Traces to Jin-dynasty poet Liu Kun's 《重赠卢谌》: 何意百炼刚，化为绕指柔 (how could steel forged a hundred times soften around a finger?). Song-dynasty 《全唐诗话》 extended the metaphor to literary revision.
memory
千锤 = a thousand hammer strikes, 百炼 = a hundred firings — picture a swordsmith forging a blade over and over until perfect.
