How well pairing works also depends on a person's personality. Introverts don't really do well in pairing situations, and especially when paired with someone totally opposite, the pairing essentially becomes a single person coding and the other person just observing and nodding their heads.
Plus beyond introversion, controlling and dominant people make everyone suffer during pairing. Also, shy people non-assertive people loose any possibility of autonomy or independent decision making (they might or might not find it uncomfortable). People who see everything in absolutes are hard to pair with and find it stressful. Extroverts who still like to think about problems silently or explore issues cant do that in pairing either.
The human social issues related to pairing are many more areas then just introversion extroversion.
Along the same lines, this doesn't work if one person is used to working rapidly and the other person takes their time to think things through. I found it only really worked best when I worked with another who worked at a similar pace to mine and we took time to bounce ideas off of each other. We both learned a LOT from each other since we both had strengths in opposing areas
