The question? "How good does a professional work of art have to be?"
More than simply asking a question that had been, unbeknown to me, begging to be answered somewhere in the back of my mind, he also provided a surprising answer. I had initially expected something catchy-but-vague, some warm and fuzzy non-answer to the question, as is the wont of successful professionals giving advice to younger aspirants.
Hubbard's answer was instead not-very-catchy (quite unwieldy in fact), practical, and in all likelihood true. What must a professional work of art have? "Technical expertise itself adequate to produce an emotional impact."
Not exactly something you'd put on a T-shirt or bumper sticker. Yet Hubbard makes a good case for it.
Without the technical expertise, you'll never be able to reach the audience with your message; if you can't convey anything to the audience, then it is not professional art - i.e. art for public consumption and not just for personal satisfaction.
Note that in Hubbard's opinion such expertise merely needs to be "adequate to produce an emotional impact" - it doesn't have to be exemplary, or sui generis. That's not to say that a writer shouldn't strive to better his craft - what it means I think is that there is always room for improvement, but once you reach the level where you can convey your message to the audience, it becomes time to buckle down and (a) think of that message; and (b) write down the damn story.
So in Hubbard's words:
A lot of artists are overstraining to obtain a quality far above that necessary to produce an emotional impact. And many more are trying to machine-gun messages at the world without any expertise at all to form the vital carrier wave.So how good does a piece of art have to be?