For me it was having to deal with overstimulation---ringing phones, too many people in my office, and constant interruptions. I don't do well with that. I need quiet and solitude to accomplish what I need to do. I also can't handle rapidly changing priorities, because I like to take on one project at a time and complete it before I go on to something else. Needless to say, I don't thrive in a fast-paced environment.