In the book, The War of Art, author Steven Pressfield talked about what separates amateurs from professionals and how a professional became who they are.
I will write about what these aspects mean to me personally.
The professional endures adversity
The pro knows the costs of being in the game. The field is never leveled, and bad lucks can rain down on him when least expected or needed. Despite all the things that can potentially go against the pro, he knows his core belief is always there and cannot be buried alive.
The professional self-validates
The pro takes control of his situation and does not allow the actions of others to define his reality. He does so by controlling his reactions and not taking the criticism personally. The pro knows that, no matter what others might say or do, he has his own work to do.
The professional recognizes her limitations
The pro knows he can never be a master of all things, rather, just one thing. He will need help in other areas, and he treats the pros in those areas with respect.