Somebody should compile a list of all the stupid decisions networks have made, because they all seem to make a lot.

Mork & Mindy (RIP Robin Williams) became the #3 show in America in its first season. Come season 2, the network (ABC) fired the entire supporting cast and changed its timeslot to go up against Archie Bunker. Even back then, most people had enough sense to know to not mess with something that worked, but you wouldn't know it from the network executives. The show was never able to recover.