In Chinese Spring and Autumn period, there lived a man in a small state named Qi.
He always spoiled his head by thinking nonsense. One day, without rhyme or reason, he even began to fear that the sky would fall and thus crash on his head and that the earth would sink and thus bury his body. He was so worried that he could neither eat nor sleep. Later, someone persuaded him that his fears were Ground-less.
A friend, worrying about his health, came to calm him. He said to the man of Qi:
The man doubted the wise man's words. He said "If the sky is really just a collection of gases all around us, what about the sun, moon, and stars? Can they fall out of the sky?" His friend replied, "No, no! The sun, moon, and stars are also made of gases and even if they fell out of the sky, they could not hurt anyone. You can relax."
The man asked, "But what about the earth sinking?" His friend answered, "The earth, including north, south, east, and west, everywhere on the earth is made of solid dirt and rocks. You can walk, run, and jump on the earth everyday. There are no empty spaces. So you don't have to worry about it falling."
Hearing this, the man was exulted in the release of his worry. The friend was also happy for him.
Background and Comment:
This idiom now is from "Lie Zi", a famous Taoism Book. This idiom now is used to satirize those who often has groundless fears.