This is REALLY simple: we don't sell any records and nobody comes to our shows. Can't get much more unsuccessful than that!
But you may say, Success can't be measured in material forms. And you would be right. Let's look at it from an artistic POV: we represent an alternative universe that never happened in which rock music matures as a cultural voice of the American people and worthy successor to Faulkner and Melville and Whitman and Hemingway and... Yeah, right! We are dinosaurs. Can't get much more unsuccessful than a dinosaur, can you?
Okay, what about judging success on a personal level like we are forced to do now with athletes, for example-- like we actually are supposed to care that the person who came in 5th had a "personal best"-- yawn-- or "did the best they could do"-- ho hum-- okay, from my personal POV-- I tell you the honest truth-- everything I do I consider to be not good enough and flawed in a hundred ways and if only I could get it right then I could quit-- and I so desperately want to be able to stop. I am so tired. So weary of it all. But, nope-- on a personal level we are unsuccessful and I must force myself onward.
Then the last criteria is whether we are successful with our audience. People profess to be moved by us in unique ways. I believe them. But now I will let you in on a Craft Secret: musicians don't trust the audience-- we know how easily they can be tricked by clever yet insincere craft techniques; we manipulate audiences, that is our job-- even the "best" of us will resort from time to time to craft technique-- so we can never really accept the love of an audience. So we are Othellos, rejecting the untainted love that is given us. Now, I'd REALLY call that unsuccessful, wouldn't you?