Ever hear the expression, "It's not what you say, it's how you say it"?
Many people who are reluctant to get up and speak fear the audience won't listen to them. They think they're not witty enough, or can't tell a joke, and if they're not funny, nobody will pay attention. Maybe they fear they don't know enough about the subject and the audience will sense it and tune them out. Or worse, they’re sure the audience knows more about the topic than they do and will be sitting in judgment and finding them wanting.
All of these beliefs are false.