The mountain top is established as a significant destination early in the book, and Simon is one of first boys to reach it. Together with Ralph and Jack, when they were still getting along, Simon had made progress along the mountain’s edge. When they reached the top, they could finally determine that they were in fact on an island.
One of the littluns speculates about the presence of an unidentifiable “snake-thing” or “beastie” that wants to eat him. Although Ralph staunchly denies that it exists, the concept expands; soon all the boys are referring to this “beast.” The fear of the unknown and their precarious situation are solidified into the idea of such a creature, but even Jack and his hunters, boys who claim to be the bravest boys, do not want to seek it out.
Simon is a sensitive, introspective boy who finds the demands of group living more taxing than the others. Although he willingly does his share, he also sometimes vanishes without warning. Showing no fear of the solitary forest, he makes his way through dense foliage and discovers the cabin-like hiding place beneath it.
By the time he decides to go to the mountain by himself, the situation has deteriorated. Ralph has tried to keep the boys together, insisting in vain that they confront their fear, so it will not overtake them. After a long discussion about its existence and possible source, Simon is the only one of the older boys to suggest they consider its reality and that it might be them.
Simon became inarticulate in his effort to express mankind's essential illness.
After Samneric sees the beast—which is actually the downed parachutist—the idea of hunting the beast gains urgency. Simon, who feels sick thinking about the heroism required to pursue it, also realizes that they will continue to squabble. After they reject his suggestion that they all go seek it atop the mountain, Simon decides that he must make the ascent on his own. In losing his fear of the beast, Simon may have lost the will to fight for survival.