We often think once someone becomes 'successful' that their self-doubt disappears... And this isn't true.
I believe that when we decide to grow and evolve and to go after more, we are always going to have self-doubt. It is part of the process.
Many people choose to stay in 'comfort' right where they are because of their unwillingness to feel the self-doubt that comes up...
Self-doubt is a part of being human... It is a natural reaction to growth.