I've never been a great public speaker, it's something that has always terrified me
Jerry Seinfeld said that the number one thing people are afraid of is public speaking... death was 2nd place. So there are people that would rather die than speak in front of a crowd. Something along those lines.
I once worked with a woman who was constantly promoted because she was married to someone high up in the company... and obvious nepotism hire. Part of her job was giving presentations to the rest of the rather huge office and she would break out into hives during every presentation. She had to be aware that this was happening and that probably made her even more nervous.
I was a class clown when I was a kid and later in life I would be involved in drama class. At one point in my life I was elected to a position where twice a year I had to give a speech in front of thousands of people, most of whom I had never met. For some reason this sort of thing has never bothered me and perhaps that is why I am the spokesperson for our bowling group.
Despite this, I can actually be quite reserved in public. I think I need a stage and an audience that kind of has to listen to me in order to be extroverted.