In the Book that I am reading called Lord of the Flies, a cultural assumption of the book is "the beast" that is in the story.
The boys think that they are not alone on the island from the beginning but they are just imagining things with their minds until suddenly, in the 7th chapter, a pilot that has crashed landed his plane died and got stuck in the branches of the trees and the boys came across it and depicted it as a "real beast".
I think that William Golding put the character of The Beast in his novel because when he was writing his book at the end of WWII, the soldiers that came home alive would have nightmares about their time in the war. The nightmares are depicted as the beast in the story at the beginning when the boys are imagining it but comes to life when the dead pilot gets stuck in the trees.
Some of the small boys were very afraid of "the beast" at the beginning of the story and had thought that they saw something on the island. The older boys said that it was just a dream but a thought came to mind that there actually was something on the island. A quote from the novel backs this up saying “He still says he saw the beastie. It came and went away again an’ came back and wanted to eat him–” “He was dreaming.” Laughing, Ralph looked for conﬁrmation round the ring of faces. The older boys agreed; but here and there among the little ones was the doubt that required more than rational assurance.
Later on the boys found the "actual beast" and were terrified of it at first but later on, all they wanted to do was kill it. Jack wasn’t as scared as Ralph facing up against the beast but he still wasn’t totally sure about it. A quote describing "the beast" states " Before them, something like a great ape was sitting asleep with its head between its knees. Then the wind roared in the forest, there was confusion in the darkness and the creature lifted its head, holding toward them the ruin of a face".
I think that the older boys would of doubted themselves after they saw "the beast" and should have believed the smaller boys from the start.
William Golding does not challenge the assumption of "the beast" because he has chosen to put it in the story as a main feature and have the boys argue over it. The beast would be a symbol of some of William's friends or even family member's nightmares after the war that would haunt them of a night.