The problem with most people's experience with pairing is that they are given no guidance on how it should be done outside of "just work with someone."

In terms of under-documentation, I didn't really find that. Most of my jobs have either been way under-documented, way over-documented (no one reads it and it gets outdated). Again I'll say that I find switching pairs daily is key with no one person stay on for more than 2 days in a row (so if a story takes three days to complete, the two people who finished it are not the same two who started it). This keeps that internal knowledge well-spread.

But you're right, if you're dealing with overly excited/stubborn folk who refuse to play ball, that's obviously not going to work. Conversely, if you have a trusting team and someone is having one of those days where they feel useless and unmotivated, pairing can turn it into some kind of useful day. This could be because your colleague gets you excited or, if you have high trust, I've literally said and had people say, "I'm not feeling it today... can you drive all day?" and you're still able to offer good support as a navigator and not have a total write-off of a day.

To the point of improving an otherwise bad day, one of the more interesting arguments against pairing I've heard is that companies use it to make sure everyone is always working. That would indeed be sad if that was the motivation.