I think GP is referring to the 100% pair programming being hell. Pair programming all the time would be hell if you didn't get to choose your partner and/or you needed time away from them for any reason. Do you really want to spend every moment programming sitting next to some other person with one of you driving and the other speaking? Every moment? Maybe if you find the right partner (I had a couple colleagues who, for all practical purposes, were always paired with each other). But good luck finding that in every office you could ever work in.