Why is Simon the only one to doubt the beasts existence lord of the flies chapter 6?

Simon is the only one to doubt the existence of the beast in chapter 6 because he is a more perceptive and introspective character. He represents goodness and insight, which allows him to question the boys' fears and see beyond their primitive beliefs. Simon's connection with nature and his spiritual nature also play a role in his ability to doubt the existence of the beast.