The door plug that blew out of a Boeing 737 Max 9 airplane was missing four bolts meant to hold it in place. They were missing because Boeing maintenance removed them and did not put them back in again.

Some workers actually made the mistake, but they were working as part of a work system that Boeing management was responsible for setting up and running. That's where the real fault is.

I suggest passing a law to require aircraft manufacturing and repair companies to have a certain fraction of licensed commercial pilots on their boards. Perhaps 66%.