Jack Black revealed it was his teacher who helped him overcome the "crippling" stage fright he suffered in his youth.
And defeating his nerves while at a school for "troubled"children in Los Angeles set him on the path to become a successful performer.
The 46-year-old comedian told The Observer Magazine: "I once tried to overcome my stage fright at school by showing up to class really high.
"'Maybe I'll discover some new level of performance', I thought. However, I just became paranoid, and even more paralysed by fear.
"The moment I managed to beat some of my stage fright demons and thought, 'This is really what I'm going to do with my life', was in a school production of The Caucasian Chalk Circle when I was 17."
Black was playing the part of an anarchist judge called Azdak when he decided he could no longer do it. But his teacher Scott Weintraub asked him to go to breakfast with him first.
"I agreed and at the diner he told me I'd been brilliant in rehearsals, and no one was going to judge me," Black said.
"Something he said gave me the confidence to go ahead.
"All my terror disappeared, and the joy of performance came back to me."
Black added he still suffers from stage fright, especially during live televised events.
He said: "Even when every fibre of your body tells you, 'This is wrong, this is terrifying, you're horrible', you can shut off that noise and just go out there. And good things can happen."