Or Heroes: Tim Kring said his original idea was to burn through charatcers in a year or so, and always have new blood. It certainly makes sense: the first season was all about characters' shocking connections to each other, and sooner or later they all meet and find out how they're connected. But NBC wanted to keep the cast, so Kring needed to come up with a new storytellign engine, one with a permanent cast. And the show still hasn't recovered from the deicision.