I dislike working in groups mainly because I don't trust people to do their work well. I also often can work faster by myself than in a group. Besides, when I work with one I either do everything... or nothing. If it's the former, I feel put-upon; if it's the latter, I feel guilty. There's no win for me.
If there's no clear leader in a group, I will lead. If there is someone who I respect who wants the position, though, I'll cede it. As a leader, I just try to make sure everyone does what they're supposed to (and if I perceive them to be slacking, I haven't got a problem with yelling at them (in public if I find them in the halls and they haven't done their job) and threatening them with death to get it done). Recently a teacher made me one of two leaders on my side of a class debate, and the other person immediately ceded all authority to me. Unfortunately, I had no idea what the various strengths and weaknesses of the group were, so I spent a lot of time asking a friend I trusted to give me opinions on placement and shuffling people. Left me with no time to do what I'm best at--research--and by the end of it I was thoroughly stressed. My side did (against the odds--it was an assigned side and had only me out of the half-dozen acknowledged "smart kids" in the class) win, though.
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cogito, ergo sum.
non cogitas, ergo non es.