In what way does the theme of regret appear within the story of Van Horssen and his mentor Verheyen?

As Verheyen's phantom pain increases, he becomes desperate and his writings reflect his Existential crisis brought on by the severe pain he is experiencing. Verheyen’s notes are a string of questions without answers: “Why am I in pain?” “Are we perhaps condemned to wholeness?” “Is my pain God?” and “What have I been looking for?” (211).