The Tang Dynasty painter Zhang Zao was renowned for his landscapes and pine-and-stone scenes. When painting, he would first sit in silent meditation; once inspiration struck, his brush would fly like lightning, ink splashing freely, and the work would be completed in moments.
A contemporary painter named Bi Hong, who had long heard of Zhang Zao's unique style of painting pine trees, asked to see it for himself. Zhang Zao agreed to paint on the spot. Holding a brush in each hand, he worked both simultaneously—one brush painting fresh branches, the other painting withered ones. The new branches seemed to glisten with spring dew, while the withered ones appeared touched by autumn frost, each with its own charm. The onlookers marveled in unison. Even more astonishing, Zhang Zao used two worn-out brushes, and when inspiration struck, he dipped his fingers in ink, rubbing and pressing them across the paper to vividly capture the ruggedness of pines, the solidity of rocks, and the flow of water.
Zhang Zao finished painting, put down his brush, and stepped away from his seat. Bi Hong approached to ask which master Zhang Zao studied under. Zhang Zao humbly replied, "I take nature as my teacher without and the heart's source within—that is all."
This means that by taking nature as his teacher and carefully observing all things in the world over a long period, he internalized their essence, allowing him to reach a state where his hands perfectly followed his mind.
Bi Hong carefully savored Zhang Zao's words, filled with both admiration and awe, and exclaimed, "Master Zhang's painting of pine trees is beyond anyone else's reach—we might as well put down our brushes from now on!" This unique technique of "holding two brushes in hand and applying them simultaneously" later became known as "shuang guan qi xia" (painting with both brushes at once), a phrase now used to describe tackling two tasks at the same time.
Source: Guo Ruoxu (Song Dynasty), *Experiences in Painting*
Meaning of the Idiom: Later, the Chinese idiom "双管齐下" came to describe how tackling two tasks at the same time.