杞人忧天 — “To worry over imaginary or groundless fears”

Once upon a time in the State of Qi, there lived a timid and somewhat neurotic man who often pondered strange and perplexing questions. One evening, after dinner, he sat in front of his door, fanning himself with a large palm-leaf fan, and murmured to himself, "What if the sky were to fall one day? Wouldn't we have nowhere to escape, and be crushed to death? Wouldn't that be such an injustice?"

From then on, he was distressed and worried about this problem almost every day. His friends, seeing him distracted and looking gaunt and pale, were concerned for him. But when they learned the reason, they all came to persuade him, saying, "My friend! Why torment yourself for nothing over this? How could the sky possibly fall? Besides, even if it did, your worry alone wouldn't solve anything. Try to be more open-minded!"

However, no matter what others said, he remained unconvinced and continued to worry constantly about this unnecessary problem. Later generations derived the idiom "Qǐ Rén Yōu Tiān" (杞人忧天) from this story. Its main meaning is to warn people not to fret over unrealistic things. It shares a similar meaning with '庸人自扰' (to trouble oneself for nothing).