While the message/theme of William Golding's Lord of the Flies is certainly realistic, the actual events of the novel, in many cases, stretch credibility. For example, we know the boys were in a plane crash and that the plane sliced through the jungle, leaving a scar; despite the violence of this action, the boys (but none of the adults) manage to get out of the plane without any harm or after effects. Just think about the logistics of that for a moment and you will know that the reader has to have a willing suspension of disbelief in order to keep reading.
Jack, the most violent boy on the island (but certainly not the only violent one) just happens to have a knife, and none of the boys other than the choir and the twins acts like they know one another, yet they were all on the plane together. There are more examples of unrealistic elements, but you get the point--and the bigger point is that these are not the things that matter.
Golding has said that he wrote this novel in
an attempt to trace the defects of society back to the defects of human nature.
To that end, what matters most to him in this novel is the degeneration of these proper and rule-abiding British school boys into murderous savages simply because he has removed all the restraints of civilization which would normally keep the worst of human nature in check. That's why he shows us Roger throwing stones at a little boy, reminding us that there is still at least a veneer of civilization on the island.
Yet there was a space round Henry, perhaps six yards in diameter, into which he dare not throw. Here, invisible yet strong, was the taboo of the old life. Round the squatting child was the protection of parents and school and policemen and the law. Roger’s arm was conditioned by a civilization that knew nothing of him and was in ruins.
Just a few chapters later (perhaps mere days in island time), however, Roger is sharpening a stick at both ends so he can make Ralph a sacrifice to the beast. This is the kind of thing that matters to Golding more than perfect realism.
So, while it is just a little too convenient to have the ship come to rescue the boys at the critical moment for Ralph, the rescue is not really the point; the rescue is just another incident which causes us to reflect on the meaning Golding intended. In this case, the question we must ask ourselves is what kind of world these little "savages" will be returning to? This is a final reminder of the war being conducted around the world, and we are in even greater despair when we realize these boys are going from one war to another, from one kind of savagery to another. The tendency of human nature to deteriorate into savagery is demonstrable everywhere, even in a rescue.