Interpreting Realism

Today my English teacher brought up a very interesting point: Is an impressionistic piece of art finished? So many times I have stood in front of a piece of art thinking 'I don't get it...'. Is not the idea of art to convey a message to an audience? So what if your audience doesn't understand? It's like reading a story in which you can't find the meaning, or listening to a violin concerto in which the accompaniment is louder than the violin. The meaning is lost. So is it the job of the viewer to interpret your art, or is it your job to convey the meaning of the piece so they can understand it?