I started my public-speaking career as a nervous introvert with absolutely no prior experience. My first live presentation was on a Disney Cruise ship in a theater that held 800 guests (and one panic-stricken presenter). I vividly recall trying to convince other crew members to push me down the steps because I was sure that if I had a broken leg or twisted ankle, they couldn't make me do it. In hindsight, I can see how silly that was.
They would definitely have still made me do it.