The Voyage of the Dawn Treader repeatedly contrasts the "real world" with the world of fantasy and magic. Like many of the fantasy novels that follow in its wake, this book develops a fantasy world that seems vaguely medieval, hosts fantastic creatures like dragons and sea serpents, and involves magic spells and powers. This fantasy world is contrasted with our "real world" of modern technology and contemporary social structures. The narrator sure thinks that the fantasy world is far better than the real one. Yet we also learn that experience in one world can function as preparation for the other, and that the real world may be more similar to the fantasy than anyone thought.
By setting The Voyage of the Dawn Treader in a world that is not industrialized or mechanized, C.S. Lewis allows the narrative to focus on the development of characters rather than the development of the world around them.
Eustace's constant need to contrast the world of Narnia with the world he comes from is symptomatic of his dissatisfaction with himself; wherever he is seems unpleasant because he makes it unpleasant.