杞人忧天 (qǐ rén yōu tiān)
In the Spring and Autumn Period (chūn qiū 春秋时期,770-476 BC), 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 falll on his head. He was so worried that he could neither eat nor sleep. Later, someone persuade him that his fears were groundless. This idioms satirizes those who worry unnecessary.