Here's why:
* He undergoes significant change: Walter starts the story as a timid, daydreaming, and somewhat passive man. He is trapped in a mundane life and uses fantasies to escape reality. However, throughout the story, he faces challenges, confronts his fears, and embarks on a life-changing journey.
* He learns and grows: Walter's journey forces him to step outside his comfort zone and embrace the world around him. He discovers his inner strength, courage, and a sense of purpose. He learns to be more assertive, decisive, and ultimately, more fulfilled.
* His relationships transform: Walter's relationship with his family and colleagues changes as he becomes more confident and engaged with his life. His wife, Cheryl, becomes his partner in adventure, and he develops a stronger connection with his fellow photographers.
While other characters, like Cheryl Mitty and Sean O'Connell, also have their own journeys, the most significant transformation is Walter's. He is the central character whose growth and change drive the narrative of the story.