俯首甘为孺子牛 is from a famous poem by Lu Xun (
鲁迅):
横眉冷对千夫指,
俯首甘为孺子牛 — 'With fierce brows I face a thousand pointing fingers; head bowed, I gladly serve as the children's ox.' This couplet became one of the most quoted lines in modern Chinese, representing selfless dedication.