Jerry Seinfeld: The secret to sit-com writing is knowing why you're doing a scene

I'm a big fan of Jerry Seinfeld's work. I really like his comedy, and I just love Seinfeld (the show), especially the really complicated structured episodes in the later seasons. I was listening to Norm Macdonald and Jerry Seinfeld. When they're discussing the improvisational nature of Curb Your Enthusiasm, Seinfeld makes a great remark about sit-com writing, that I think applies to writing in general. 

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He argues that you have to know why you're doing a scene and that the entertainment comes from this idea:

Norm MacDonald: But do you think- Let's say there's a scene on Curb your Enthusiasm, it's Larry David and John Farley, and somebody else. And they're told to show-up at a bowling alley. Don't you think Larry comes in with some jokes in his head? Is it all improvising from Larry's part?

Jerry Seinfeld: Well, I think he knows what the scene's about. Why it's a funny scene. And that is 90 percent of good sit-com writing: it's WHY are we even doing this scene? If you can answer that question with a funny sentence, you're on the right track.

If the answer is: well, so he can meet the mother-in-law, and then find out lat-- No. That's not funny. It's that there's got to be a reason in the scene: that it's funny that we're even here.

This is something that we learned over the years. Larry and I didn't know anything at the beginning. But we learned over the years that's it's like, if you can answer that question: why are they in this bowling alley? What's the reason? It better be something funny. And then the jokes will sit on that. But if it's, well it will be funny when-- No.