Got this response on another forum that makes sense to me.
Originally Posted by Haphazard
Humor has to do with a brain misfire, I've heard.
It sets up a situation that makes sense and that veers off route. This is part of the idea that 'situation and then something unexpected'. It's also situational comedy, because where something is in the situation that's known as normal to an everyday person, it can proven absurd by the comedian. Again, brain misfire. Then you laugh.
What tends to be even funnier is the disconnect between two things that make sense, but connect between in nonsense. That's how most jokes go, anyway. The punchline is funny not because it's nonsense, but because it's unexpected and yet still makes perfect sense.
Or something like that.