Simon doubts the existence of the beast because he is the most clear-sighted of the whole group of boys. He is more intellectual, able to think things through, and able to rise above crude emotions of fear or fascination. The other boys appear rather childish in comparison, still believing fearfully in the existence of external monsters, of the kind that appear in fairytales, whereas Simon realises that the real monsters of fear and lust and violence are to be found within human beings themselves. Despite his depth of understanding, however, he is not able to prevent the group's descent into savagery. He symbolises the clear-thinking, rational side of human nature, as opposed to emotion and instinct.
Lord of the Flies reveals the endless possibilities when human nature is tested to its limits. William Golding, the author, maintains that man is most likely to descend into savagery when the limits of civilization no longer apply. The boys in this novel find themselves alone, with no "grown ups" on an "enchanted" island. Despite Ralph and Piggy's best efforts to form a democratic-like society with rules and with Ralph as an elected leader, they prove no match for Jack and his hunters whose fascination with hunting pigs turns into something far more sinister as they lose control and forget everything they were taught. At first, Jack agrees that "we're not savages. We're English..." (ch 2). This foreshadows the tragic events that will follow as Jack soon forgets what is right and what is wrong in the frenzy of the hunt and the kill. Even Simon's deeper understanding of their surroundings, and his ability to recognize the boys' own insecurities, is not enough to save him.
The "littluns" are the first to express their fear of the "snake-thing" which, after Simon admits to sneaking around at night and, unwittingly, being the cause of some of the fear, evolves into a physical being which even Ralph thinks he has seen, with "teeth...and big black eyes" (ch 8).
Simon has never been scared of a beast, only the developing animosity between the boys. It is Simon who senses the competitiveness between Ralph and Jack and the changing atmosphere. In chapter 4, after Jack has allowed the fire to go out but has also caught his first pig, Simon "looked from Ralph to Jack...and what he saw seemed to make him afraid." It is Simon's intuitive outlook which allows him to recognize the changes in the boys. In chapter 5, Simon tells the boys, "Maybe it's only us." He tries to express himself and describe "mankind's essential illness" but he is misunderstood and the boys become fixated on the possibility of ghosts.
Simon's own revelation comes in chapter 8, when he faces his own fears as the pig's head which Jack and his hunters left in the forest brings forth "that ancient, inescapable recognition." Simon is so overwhelmed he loses consciousness, presumably from a fit. On his way out of the forest, Simon discovers the body of the parachutist but his efforts to inform the others are no match for the representation of the beast. Ironically, Simon is mistaken for the beast and his death signifies the end of rational thought. Even Ralph and Piggy are unsuspecting participants in his death.