Gu Yong, courtesy name Ziyun, was a native of Chang'an (present-day Xi'an, Shaanxi) and served as an imperial advisor and Minister of Agriculture under Emperor Cheng of the Han Dynasty.
Emperor Cheng of Han ascended the throne at twenty, but by his forties, he still had no heir. He fell under the sway of alchemists, becoming obsessed with sacrificing to ghosts and gods. Anyone who presented memorials on these rituals or the path to immortality was swiftly rewarded with high office and lavish gifts. Trusting their advice, the emperor poured immense funds into grand ceremonies at the Shanglin Park outside Chang'an, begging heaven for blessings—yet nothing came of it.
Gu Yong admonished Emperor Cheng of Han, saying, "I have heard that those who understand the nature of heaven and earth cannot be deceived by spirits and monsters, and those who grasp the principles of all things cannot be misled by those of crooked conduct. Now some people grandly speak of immortals and ghosts, extolling sacrificial rites, claiming there are celestial beings who take elixirs of immortality and live as long as the Southern Mountains. Their words paint a vivid picture, as if one might meet a god at any moment—yet when you seek it, it is as elusive as trying to bind the wind or capture a shadow. That is why wise rulers of old ignored such talk, and sages never uttered a word of it."
Gu Yong then offered more examples: "In the Zhou Dynasty, the historian Chang Hong tried to help King Ling of Zhou by using sacrificial rituals to summon the feudal lords to court, but the Zhou royal house only grew weaker, and more lords rebelled. King Huai of Chu held grand ceremonies to honor ghosts and gods, praying for divine aid to repel the Qin army, yet he lost the battle, saw his lands carved away, and ended up a prisoner. After unifying the empire, the First Emperor of Qin sent Xu Fu with boys and girls across the sea to seek immortals and the elixir of life, but they never returned, earning him the hatred of all under heaven." He concluded, "These examples show that relying on spirits and rituals only leads to ruin, not success."
"From ancient times to the present, emperors, relying on their noble status and abundant wealth, have searched the world for gods and immortals, spending countless years without any response. I hope you will no longer allow those of improper conduct to interfere in court affairs."
Emperor Cheng of the Han Dynasty found Gu Yong's reasoning compelling and decided to follow his advice.
Later, the idiom "catching wind and grasping shadows" came to describe speaking or acting without factual basis, or making something out of nothing.
Source: *Book of Han*, Chapter "Treatise on Sacrifices"
Meaning of the Idiom: Later, the Chinese idiom "捕风捉影" came to describe how speaking or acting without factual basis, or making something out of nothing.