What is the relationship between realism and fantasy in the story? What are some details that make the fantastic story credible?

We can certainly take this story as a metaphor in Gregor's attempt to escape his job and bondage to his family. Alone in his room, Gregor tries to rebuild the self-identity that he had lost by living entirely for others and ignoring his own needs. He cannot, however, escape from what he sees as his family duty, and continues to act only to serve his family by doing his best not to inconvenience them. Gregor's comments about his family's behavior are often tinged with resentment at the way they treat him, but he will not allow himself to recognize his bitterness. Gregor manages to escape his self-effacing sense of duty only in the last chapter, when he asserts himself in realizing that his family has been neglecting him. Gregor's search for his identity seems hopeless, however, because he never had an identity to start with.