【Explanation】: "Lí" refers to a black dragon in ancient times. The phrase means obtaining a precious pearl from under the jaw of the black dragon. Originally, it described taking a great risk to gain a great reward. Later, it came to metaphorically describe writing that is profound in meaning, concise in expression, and which captures the essence of the subject.
【Source】: *Zhuangzi·Lie Yukou*: "Bring me a stone to forge. A pearl worth a thousand pieces of gold must lie in the depths of a ninefold abyss, beneath the jaw of the black dragon. You were only able to take the pearl because the dragon was asleep. If the black dragon had been awake, what chance would you have had?"
Long, long ago, there was a family living by the Yellow River, making a meager living by cutting reeds and weaving mats and baskets. They lived in great poverty.
One day, the son was cutting reeds by the riverbank. The sun beat down fiercely, making him dizzy and faint, so he sat down to rest. As he gazed at the river shimmering with ripples in the sunlight, he remembered his father once saying that many treasures lay in the deepest part of the river—but no one dared go there, because a fierce black dragon named "Lí" lived in those depths. The boy thought, "If I could dive to the river bottom and find a treasure, my family wouldn't have to work from dawn to dusk and still go hungry. I might as well take the risk and try." With a determined heart, he quickly stripped off his clothes and plunged into the cold river.
At first, he could still see small fish swimming around him. But as he swam deeper, the light grew dimmer and the water colder. Finally, he could see nothing—complete darkness surrounded him. He began to feel afraid, unsure of which way to go. Just then, not far away, he spotted a round object glowing faintly. He looked closely—ah! It was a luminous pearl! Holding his breath, he swam toward it, wrapped his arms around the pearl, and with a strong tug, pulled it free. He quickly surfaced, scrambled ashore, and ran all the way home.
When his father saw the pearl, he immediately asked where his son had gotten it. The boy recounted the entire story in detail. After listening, his father exclaimed, "How dangerous! That pearl worth a thousand pieces of gold grows beneath the jaw of the black dragon. You could only have taken it because the dragon was asleep. Had it been awake, you wouldn't have stood a chance!"
This story is recorded in *Zhuangzi·Lie Yukou*. The idiom "Tàn Lí Dé Zhū" (probing the black dragon to obtain the pearl) later came to symbolize writing that tightly grasps the central theme and captures the essential point—concise, powerful, and profoundly insightful.