While talking to a friend (a man can hope can't he?) about stories I mentioned how I would make up alternate endings or fill in character motivations. He asked if that was a big part of the story and I remarked in a rare moment of clarity that, for me, that sort of thing is the story.
If a song is sad I tell myself why. If I find a character in a movie interesting, I might envision a few extra scenes for them. And, of course, we've all had that moment where we come up with some fiction for why people behave in real life.
Another aspect of art is that the importance or motivation that we place on some things are completely out of proportion to what the artist may have intended. There's the interview with the singer who, it turns out, does not actually write their own songs. The star who does not behave at all the way that we think they should based on their performance in a movie.
Like a Rorschach test, the meaning we place on art is more indicative of the reader/viewer/listener than it may be of the art itself.