Originated in feudal times, scholars had to take the imperial examination if they wanted to be an official. In the Ming dynasty, exams were very difficult. If you are accepted, you will put up a flagpole in front of the door. If you fail in the exam, take off the flagpole and take it away. This is called "bad luck". "lintel" is the crossbar on the door, which means high pole here. The pronunciation of "mei" and "mildew" is similar, so people in Jiangsu and Zhejiang provinces call it "unlucky" or "unlucky"