When Ralph realizes that he is on what resembles Ballatyne's Coral Island, he is thrilled, casting off his clothes in a gesture symbolic of his rejection of the restrictions of the life at the boys' school from which he has been evacuated. But, it is the voice of reason in Piggy, who immediately is concerned that order be established. However, he is ineffectual at creating this order because of his physical appearance--he has thinning hair like an older man, and also more like an older man, he is fat--and because it is Ralph who finds the conch and blows it, summoning the other boys. Moreover, Ralph seems more suited to the role of leader because he is "the golden boy," handsome, confident, and appealing as a model to the others, while Piggy is intimidated by the appearance of the red-haired Jack Merridew, leader of the choir in his formidable black uniform.
Along with Piggy's physical appearance which works against him, there is his apparent weakness as evinced by his intimidation of Jack. Certainly, with his asthma and extra weight, he cannot compete against the more athletic boys such as Ralph and Jack. For, example, when the boys make a rescue fire, Piggy arrives too late to assist with this work. And, while he is more rational than the others, he is unable to put into action some of his more reasonable ideas because Jack heckles him, telling him such things as that the conch has no significance on the mountain, thus undermining Piggy's authority to speak. Later, he berates Piggy when he criticizes both him and Ralph in Chapter Eight,
“[Ralph is] like Piggy. He says things like Piggy. He isn't a proper chief.”
Jack alludes to Piggy's criticisms of the "small fire" that got out of hand, and other disparaging remarks that he makes after something has happened. Besides Piggy's negativity, the indiscriminate power of brute force works against Piggy. For, the young boys ignore Piggy's warnings and urgings because the stronger Jack intimidates them; Jack cruelly takes Piggy's glasses from him; and even Ralph succumbs to the seduction of the hunt, leaving Piggy alone.
Certainly, the "white magic" of the conch does not maintain order on the island. Later, Piggy and Ralph talk with one another. Ralph asks in Chapter Eight,
"…I mean…what makes things break up like they do?
Piggy rubbed his glasses slowly and thought […].
"I dunno, Ralph. I expect it's him."
"Jack." A taboo was evolving round that word too.
Ralph nodded solemnly.
"Yes," he said, "I suppose it must be."
But, it is not Jack alone who is the reason that Piggy and Ralph are ineffectual. There is a rebellion in the boys against authority and science, which Piggy represents with his rational thinking, older appearance, and glasses. Without any accepted symbols for authority, the boys attempt to use the conch, but the rebellious Jack and the sadistic Roger ignore such things as the conch and Piggy's glasses and adult appearance. As Simon discerns, it is the "beast" within them that drives the boys to act as they do, the inherent evil in their human nature. Indeed, it is this inherent evil which the rules of society no longer deter that drives Roger to ignore Piggy as he urges the hunters to stop their savage actions and, instead, unleash his sadism by unleashing the granite rock upon Piggy, hurling him down the mountain into the bloody water, representing the end of reason and foreshadowing the bloody injuries and murderous attempts upon Ralph.