I think a lot of my deep thoughts come subconsciously. My biggest leaps of insight happen when I've taken some time - hours, maybe days - away from a problem.

I've found this to be true of many pursuits: programming, writing fiction, even things like "where should the fridge go when we redo the kitchen?"

What you're talking about, good responses in the moment, isn't about deep thought, it's about being witty. They're different problems.

And I suspect that a lot of the people you think are being clever in the moment are actually repeating fragments of conversations that they've had with themselves in private. This isn't universally true, of course, but I do think it plays a part.