When I went to Los Angeles right after high school, I got some acting jobs, and I never, ever wanted to be an actress! Public speaking and acting make me want to vomit. But I have never been nervous singing. When it comes to public speaking, I stumble on my words, sweat, and pull at my clothes.
We don't always have an accurate view of our own potential. I think most people who are frightened of public speaking and can't imagine they might feel different as a result of training. Don't assume you know how much potential you have. Sometimes the only way to know what you can do is to test yourself.