That was Le Tai.
In 1504, the court held the Highest Imperial Examination to select new talents to lead the country. Two brothers, Le Nai and Le Tai, left for the capital to take part in the exam. Le Nai was a composed person and applied himself to learning. However, his younger brother, Le Tai, was very intelligent but quick-tempered and impulsive; he did not immerse himself in his studies. Finding the literature test difficult, Le Tai asked for his older brother's help. Le Nai refused, saying, "We're in the examination. It's not fair if I help you".
Le Tai became angry and left the examination room. On the way back home, he realised his bad behaviour and felt ashamed. By the time he reached his house, darkness had settled over the village. He did not dare wake everyone, so he slept on the threshold.His mother got up at midnight, when the moon was shining brightly, opened the door, and found Le Tai. Guessing that her son had troubles, she woke him gently and fed him. But Le Tai did not care about eating; he immediately plunged headlong into study. On seeing this, his mother shook her head, saying, "You're too erratic. You work hard today, but you may stop tomorrow. You will never succeed without regular study.""I've already thought about this". Le Tai replied, his voice determined. "I promise I'll study seriously and diligently from now on."
In order to validate his promise, Le Tai pointed to the moon and said, "The moon above is my witness."
Indeed, Le Tai did apply himself to his studies. Sometimes he felt tired and wanted to relax, but the bright moon motivated him to work harder. After much effort, Le Tai passed the Highest Imperial Examination in 1510.