The trademark of a real professional is the spirit of service above self. You are here to enrich the world, and you impoverish yourself if you forget your errand. Many years ago, Jerry Harris of the Detroit Free Press wrote an interesting column. What follows is part of his answer as it relates to professionalism. Anyone can write when inspiration strikes them.
Any composer can be jolly when conditions are favorable.
Any actor can be self-possessed if he is well, and well paid. The word professional has taken on a purely mercenary meaning in our times. It should not just mean someone who earns a living at a particular craft, but someone who professes his devotion to a calling, beyond the needs for pleasure or for profit. Beneath the long, straggly branches of an old willow tree. Disillusioned by life with good reason to frown, For the world was intent on dragging me down.