I am the exception that proves the rule

I am the artist performing on the stage,
I am the tiny bird trapped in a cage,
I am the firefly that isn't very bright,
I am the spirit of a moonless night,
I am the song that was never sung,
I am the bell that was never rung,
I am the athlete who lost the race,
I am the stranger without a face,
I am the book that was never published,
I am the lamp whose light has diminished,
I am the oddity, I am the fool,
I am the exception that proves the rule.