"Black hair doesn't know how to study early, and white head regrets how to study late" is a beautiful sentence in "Persuade Learning" written by Yan Zhenqing, a great calligrapher and poet in the Tang Dynasty. The whole poem is: "The lights are on at five o'clock in the middle of the night, just when men are studying. Black hair doesn't know how to study hard early, and Bai Shoufang regrets studying late. " "Black hair doesn't know how to study hard early, and white head regrets how to study late" means: If you don't know how to study hard and study hard when you are young, I'm afraid it's too late to know how to study hard when you are old, and it's too late to regret it.