In high school I got pushed into public speaking opportunities by my teachers. I was as uncomfortable as anyone I suspect, although I never quite understood the level of anxiety and fear that others report.
One of my early experiences came from a high school science fair. A classmate and I took first and second place in St.Louis in the spring of 1971. One of our rewards was a trip to the Marshall Space Flight Center in Huntsville, Alabama to compete at the regional level. For a science fiction fan (a proto-nerd before the term became popular), this was akin to an invitation to the Vatican. I didn’t advance any farther, although I did wangle a private backstage tour because my advisor had professional connections to the staff there.
We got feedback from the judges after our presentations. The bit that sticks in my mind fifty years later was an observation that I handled the Q&A session much like an experienced engineer.
As a consultant, and later a professor, I’ve spoken in front of audiences in Beijing, Prague, and Stratford-on-Avon. I know my way around a stage and with an audience.
All of which is built on practice and repetition. Scarcely a new observation.
Familiarity breeds comfort not contempt.