I seek out things that terrify me, like an improv class. I'm terrified of sharks, but I scuba dive. I'm not good at auditioning, but I force myself to do it all the time. I've never met anybody who is fearless, but the more you push against your own boundaries, the easier it becomes to push.
I had a Spanish teacher in high school. I rarely got in trouble in her room because I felt I was disappointing her if I got a bad grade. That had more power over me than teachers who told me I talked too much. That level of respect I had for her made me not want to fail for her.