Examine if Stevens is the protagonist or an observer in the story.
I think that one can make the case that Stevens is the protagonist who recognizes his own faults because he simply was an observer when he should have been a participant. Part of what makes his characterization so compelling is that he recognizes that his own lack of acting upon his emotional sensibilities has caused him to miss out on tremendous opportunities. His construction as a butler both in profession and in character has rendered him as simply a butler in life, as well. He is an observer in his feelings towards Miss Kenton and to what he knows is right, but stifles its expression in accordance to what duty tells him to do. Stevens is the protagonist, but he is one who painfully learns how much life is lost in living when being an observer becomes the mode of being in the world. For Stevens, his condition as the protagonist is one where we, as the reader, understand the painful condition of living life as an observer when our sensibilities compel us to act. Stevens is the protagonist that sheds illumination to the dangers of merely observing when action is warranted.