Reading all that, I felt an echo regarding my job. OK, when I get something wrong, nobody dies. But it (sound engineer, i.e. the bloke at the desk in the middle of the auditorium) is a "high stress" job. When it goes wrong, everyone in the audience looks at you, and the client wants to know what you did wrong.
So the same things apply: if you're going to do the job, know that you can do it, and make sure your really can do it. Be relaxed and confident, and never lose your concentration.