[darkwater]

As others pointed out, for many of us pair programming is much more demanding on mental resources. The way I tend to work is by doing micro-breaks, checking out other things I would not be comfortable sharing with someone else; if I don't do that and keep hyperfocused, I get drained quicker. Also you can get a couple of programmers that will go down the wrong rabbit hole for much more time because they reinforce their wrong belief mutually. This obviously happens with individuals as well but if you get the wrong mix it can be much worse.

[darkwater]

Also to expand on this, personally I found pair-programming easier on my mind when done IRL and not remotely. Sitting one next to the other has just more bandwidth available and spreading the communication over it makes it way easier for me. Remotely, I can do it for a 2, maybe 3 hour session and then I'm fried for the rest of the day (but usually those were 2-3 good and productive hours).