“It is one thing to study war, and another to live the warrior’s life” - Telamon of Arcadia, mercenary of the fifth century B.C.
The biggest difference between an amateur and a professional is that an amateur has been defeated by Resistance, but a professional has conquered it. While the amateur plays for fun, the professional plays as a vocation - this means that the professional pursues his calling twenty-four hours a day, seven days a week, whereas the amateur is more of a weekend warrior.
Apply principles from workday lives to your artistic aspirations
Follow the traits of a professional artist, not an amateur one.