I took public speaking in undergrad and part of my Professional MBA program. I thrive on public speaking. The biggest speech of grad school I wrote 5 minutes before class and improvised half. I got an A and the teacher asked if I would mind sharing with class how I prepared so well. I then told him about writing it 5 minutes before class and he asked me not to share. The lesson here is that I knew my material well enough to feel confident in my public speaking but some of that is natural ability.