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 Ground-less.

This idiom satirizes（讽刺，挖苦） those who worry unnecessarily.