I think it's natural for a piece of art to escape the artist's control; it's the result of a piece of work producing a reaction. While the levels of meaning in artistic expression may sound logical from a theoretical point of view, I think art is not ruled by such strict parameters. Otherwise a lot of what is considered art wouldn't be such. There are pieces of art which don't convey any special meaning, are merely representative but do cause an emotional response on the spectator, others which do try to convey a certain meaning and still others where the spectator's interpretation is paramount for the art to make any sense.
While I can understand the artist's anxiety about his/her piece conveying a certain meaning, there's nothing he/she can do if people don't understand it the way it was meant. In that case the artist needs to examine where he/she went wrong, if the interpretation of a particular meaning were important. What I mean to say is that the artist's explanation/justification/public judgment of a piece does not add, but rather subtracts from the experience someone as a spectator establishes with that piece of art.
I'm explaining what I think and feel about my own work, I really feel any piece of art must convey a meaning, but when I say meaning I say it in a very broad interpretation, of course an emotional reaction is meaning for me, and most of the times I try to express emotional states and not ideas, every artist is compelled to express different things, I know I can't do anything if people don't understand me, what I try to explain is that one of my parameters to establish if my work is good or not is if people understand what I want to say with any determinate piece or if I get from them the reaction I was aiming to, and although I love people finding different things in what I do, sometimes things I have never thought about before, I hate it when they don't get my "message", and I hate it because it reminds me how far I am from being the artist I would like to be, because it is my way of communicating, it's not only the aesthetic part involved, it's a kind of necessity I feel deep inside.
The theory about the 3 meanings is a simplification, but I find it very useful to explain why art judging is not objective., we could also speak about taste, tradition, culture and many other parameters, of course.
When I say that sometimes your work escapes from control I'm talking about the production process, sometimes I have an idea of something I want to transmit and I start working about it, but what comes to the surface is a very different one, it is like something appearing from my subconscious, in many cases I can't do anything to change it, it's usually better if I don't do anything, I live it like a gift, something that comes to me, I don't know if I have explained it clearly enough. After the piece is finished and thrown to the world, it has its own life, so to say.
I feel very egocentric talking about myself this way, what I wanted to explain with examples is why the artists judgement of their own art is so different from the spectator's, they aren't going mad as someone said before, it is a very complex process, every person would use different parameters, I don't believe mine are the universal for every artist, but they can be very, very different from what the public are judging.
Finally, to get back on topic, I think that U2 relationship with their own work is a healthy one, every one in the band has different opinions about songs, different favourites and that's normal, they are four people, not one, and, of course, their favourites don't have necessarily to be the ones from the audience.