Many people in the world have fear of public speaking.
It is called glossophobia and it is not just about public speaking. It's also about any public performance as singing, dancing and doing anything when a lot of people are watching you. Usually you claim that you are self-confident but it seems that's only when nobody is watching. Once I listened a political speech performed by an extremely unexperienced person and I felt how his voice was shaking and noticed his pale face. This kind of performance didn't encourage the speaker because he didn't made the public interested for what he had to say. When I came closer, I noticed the stain on the suit of the speaker and I realized that the person vomited just few minutes before the speech and forgot to clean his suit.
This person actually had something smart to say but of course that he ended very low on the rank list after the elections. It seems that for people who watch you is more important "how to say" than "what to say". A good speaker can manipulate crowds, no matter of morality of his intentions. That's why we have today a lot of smart and capable people who never seized the opportunity and they just stayed on their start points without any progress in their lives only because they are afraid to speak up!
So what's the cause of this "glitch" in human behavior?
Well, you can't just come in front of the crowd and act like all that is natural to you if you didn't have any experience before that. Maybe once, a long ago, you had to read some text in front of your whole class and they all were mocking at you because of bad pronouncing or something... And that left the mark in you for your whole life.
Many people simply can't do it because they never had a chance and they can't relax when they see that everybody watch them. It's easy to say something in front of those people that you know well and see them every day, but it is not always like that. Sooner or later you will be forced to say something in front of the bunch of people and you don't have idea who they are.
I think that he fear of speaking in public comes from a much more simple feelings.
Some people have a trouble when they have to ask someone for direction. Or when they have to stop an unfamiliar person and ask for the time. Interaction with unfamiliar people can be a great exercise for those who have problems with speaking in public. Be completely careless and just start talking. The point is to be relaxed and not to care about what those people will think about you. That can cause you a pressure.
Some of us are naturals!
I say "us" because I never had problems by doing anything in public. I was never some shy boy, I never hesitated to approach unfamiliar people or the girls that I liked. In one point of my life I realized that I was like born with a microphone in my hands. The more people I see from the stage, the more powerful I feel. But tI had to work for that! Work a lot!
Drinking alcohol is the worst way to deal with the public performance fear.
Alcohol will reduce your fear but it will also reduce your ability to do on the stage all as you planned. And you could say what you don't want to say, so when you get sober, you will realized how embarrassing it was....
I had a specific problem with an "energy vampire" on the stage. We had some band member that always wanted to dominate on the stage, he was interrupting the others and made many uncomfortable situations to us. I know that person since I was 13 and my first time on the stage was with him so I kinda thought that was normal. And I didn't feel comfortable on the stage because he was speaking in my name and in the names of others. When we got rid of that guy, it was like we got some extra space on the stage, the space for all of us. So sometimes it is not problem in you, or in people that you don't know, sometimes the problem is in those who are close to you!