  The Man of Qi who Worried That the Sky Would Fall 杞人忧天

  In the Spring and Autumn Period, in the State of Qi there was a man who always let his imagination run away with him. One day he even worried that the sky would fall on his head. He was so worried that he could neither eat nor sleep. Later, someone persuaded him that his fears were groundless. 
  春秋时代，杞国有一个喜欢胡思乱想的人。一天，他竟然想到，天会塌下来，地会陷下去，自己到哪里去安身？这个人越想越害怕，整天愁眉苦脸，坐立不安，白天吃不下饭，晚上睡不着觉。后来有人耐心地开导他，他才放下了心。

  This idiom satirizes those who worry unnecessarily.
  "杞人忧天"这个成语讥笑那些没有必要或毫无根据的忧虑。