Once upon a time, a man lived in the state of Qi was really timid and often got absurd ideas. One day after dinner, he went to relax at his doorway. Suddenly, he thought, "If one day, the sky falls down. We will be all crushed to death." From then on, he was bothered by this thought constantly. His friends really worried about him, and suggested him to be more open-minded. They talked to him that the sky wouldn't fall down and even if it would, it would not be a problem he can solve. However, no matter what was said to him, he still worried about this unnecessary problem.
Explanation 胆小dǎnxiǎo：timid（ adj. ） 乘凉chénɡliánɡ：to relax in a cool place（v.） 塌tā： collapse（v.） 从此cónɡcǐ：from then on（conj.） 烦恼fánnǎo：to bother about（ v.） 劝quàn：persuade （v.） 解决jiějué：solve（v. ） 不必要bú bìyào：unnecessary（adj. ）
"杞(Qǐ)" is a name for an ancient place. "忧(yōu)" means worry. “杞人忧天(Qǐrén Yōu Tiān)” means that a man lived in Qi worried about the sky would fall down. It refers to unnecessary or groundless worries and anxieties.
Scientists agree that the doomsday is not entirely 杞人忧天. If we don't pay attention to environmental protection, the ecological system will become worse and worse and the end of the world will finally come.