Psychology: The Impostor Phenomenon

The Impostor Phenomenon was first recognized in the 1970s by two psychologists name Suzanne Imes and Pauline Rose Clance. People with Impostor Phenomenon or Syndrome find that they are always waiting for their latest success to be torn from them as if they don't deserve it. It's more common than many people think. Often, these self-doubts of high successful people are internalized. Even those around them do not know that there's a fear and internal self-doubt because it's kept inside. http://paulineroseclance.com/impostor_phenomenon.html

The Cause
While there doesn't seem to be a root cause that can be pinpointed for the phenomenon, it comes from people who feel they are undeserving of their success. It happens to actors and actresses frequently.
The real advances come when you advance in your career whether you have fear or not. You can't let it hold you back. Many times the real impostors do not have any self-doubts.

Skills and Experience
Take a real look at your skills and experience. Of the actors and actresses who admit to feelings of being an imposter, it was the ones who have tons of awards from their peers and the public that seem to have it the worst. Maya Angelou who was an honorary doctorate with over 50 degrees as well as a poet, writer and filmmaker once said that even after she'd written eleven books, she thought that she would be "found out" as if she'd run a game on people. http://www.mayaangelou.com/biography/

Feedback
It can be hard to believe those around you because it may feel as if they are biased. You can find other professionals and mentors who will give you candid feedback about the parts of your work that make you feel like an imposter. It can help to seek help from a mental health professional if you feel the negative thoughts might be holding you back from success.