In Chapter 11 of Lord of the Flies, Piggy's glasses have been stolen, and Jack controls all the boys on the island except Ralph, Piggy, and Samneric. Piggy is in a desperate situation since his eyesight is so bad; he will be almost completely disabled now. Piggy and Ralph decide they must confront Jack with the immorality of what he has done. They plan to take the conch and call an assembly; they will try to reason with Jack through logic and appeals to "what's right." Ralph's idea is to make themselves look respectable--to wash and appear civilized. They want to draw a contrast, to display visually the superiority of civilization and rules to savagery and chaos.
The error of this plan is that Jack and the boys who follow him have regressed beyond the point where morality and authority can influence them. They have formed a new society that no longer recognizes the rules that once bound them. Thus, although they come at the sound of the conch, they reject the order that it once represented to them. They have no sympathy for the terrified, disabled Piggy who kneels before them. When Ralph shouts, "Thief! Thief!" if produces anger from Jack, not remorse. Piggy's attempt at reasoning with them through rhetorical questions fails completely. Each time he presents the two alternatives, civilization or savagery, the boys respond by throwing rocks. They respond to negotiation and reason with violence. The reason Piggy and Ralph' plan does not work is that Jack's society has deteriorated to the point where normal arguments based on logic and morality cannot affect them anymore.