捕风捉影 — “To make groundless accusations or statements”

Gu Yong, courtesy name Ziyun, was a native of Chang'an (present-day Xi'an, Shaanxi Province). During the reign of Emperor Cheng of Han, he served as Guanglu Dafu and Da Sinong. Emperor Cheng became emperor at the age of twenty, but even in his forties, he still had no children. He was easily swayed by the words of alchemists and became deeply involved in worshipping spirits and deities.

Many who submitted memorials to Emperor Cheng discussing sacrifices to ghosts and gods or advocating for immortal doctrines easily attained high official positions and generous emoluments. Emperor Cheng, believing their words, organized elaborate sacrificial ceremonies in the Shanglin Garden outside Chang'an, praying for blessings from heaven. This incurred enormous expenses but yielded no discernible results.

Gu Yong submitted a memorial to Emperor Cheng, stating: "I have heard that a person who understands the true nature of heaven and earth cannot be bewildered by supernatural phenomena; one who comprehends the principles of all things in the world cannot be deceived by immoral individuals. Currently, some people extensively discuss immortals and spirits, promoting various sacrificial methods. They claim that immortals exist in the world, consuming elixirs of immortality and living as long as Mount Nan. Listening to their words, one's ears are filled with beautiful prospects, as if one could meet immortals immediately. However, if you try to seek them, they are ethereal and elusive, as impossible to grasp as trying to bind the wind or catch a shadow. Therefore, the wise kings of ancient times did not heed such words, and sages would never utter such things."

Gu Yong further provided historical examples: During the Zhou Dynasty, the historian Chang Hong attempted to use sacrificial rituals to spirits to assist King Ling of Zhou, hoping to gather all the feudal lords for an audience. However, the Zhou royal house only declined further, and more lords rebelled. King Huai of Chu meticulously offered sacrifices to spirits, seeking divine protection to repel the Qin army, yet the war was lost, territories were ceded to Qin, and he himself became a captive. After unifying China, Emperor Qin Shi Huang dispatched Xu Fu with young boys and girls to seek immortals and gather herbs overseas. However, they never returned, leading to widespread resentment throughout the realm.

Finally, Gu Yong concluded: "From ancient times to the present, emperors, with their esteemed status and abundant wealth, have searched the world for spirits and immortals for countless years, yet there has been not the slightest verification. I sincerely hope that Your Majesty will no longer allow those immoral individuals to interfere with court affairs." Emperor Cheng found Gu Yong's words profoundly reasonable and consequently heeded his advice.