The sitcom as tragedy: Because the status quo must be upheld, man is unable to grow beyond his flaws and thus always doomed to failure.
Both tragedy and comedy are built on humanity’s flaws. In tragedy, the flaws doom men to a terrible end. In comedy, the flaws bring amusement and really don’t matter. But that also brings its own sorrow to it, at least in the strictly episodic sitcom structure–these characters must remain recognizable and amusing, so their flaws can never be totally overcome, and their grand plans to change their lives can rarely work. In tragedy, man’s flaws destroy everything. In comedy, man’s flaws mean that things always stay exactly the same.