Why is Simon the only want to doubt the existence of the beast in Lord of flies?

Simon doubts the existence of the beast because he possesses a deeper understanding of human nature and recognizes that the true source of darkness lies within each individual. He represents the voice of reason and spirituality in the novel, contrasting with the other boys who are consumed by fear and violence. Simon's introspection and connection to the natural world make him more inclined to question the existence of a physical monster, as he sees the real threat as the inherent evil within themselves.