When I was self-studying social psychology I came across social facilitation theory and found it applicable to understanding interviewing. People have a hard time performing complex tasks while other people are watching because their working memory is monitoring the social situation. This varies for each individual. For tasks that have been rehearsed, like a musical or dance routine, they perform better. Politeness theory is applicable as well, people want to be liked and at the same time do not want their autonomy challenged. My pet theory is that the whiteboarding epidemic is a status hierarchy game essentially communicating "if you want to work here, you are going to do what I say."