Professionalism in art has this difficulty: To be professional is to be dependable, to be dependable is to be predictable, and predictability is esthetically boring - an anti-virtue in a field where we hope to be astonished and startled and at some deep level refreshed.

This quote is saying that when it comes to art, being professional is difficult because professionals are expected to be reliable, meaning they usually produce work that is the same or similar. But when it comes to art, we want to be surprised and amazed. Being dependable makes the art predictable and uninteresting, which goes against the idea of art being refreshing and impactful.