Final answer:
Jack attacks Piggy out of frustration with his ideas, resulting in Jack breaking Piggy's glasses and symbolizing a descent into savagery while leaving Piggy nearly blind.
Step-by-step explanation:
In William Golding's novel Lord of the Flies, Jack attacks Piggy because of frustration with Piggy's ideas and his influence amongst the boys, which is indicated in the broader narrative of the novel. During this attack, Jack breaks Piggy's glasses, which is a pivotal moment because it symbolizes the further descent into savagery and represents the further breakdown of order and reason on the island. Piggy's glasses are symbolic of civilization and rationality, and damaging them has the practical effect of rendering Piggy nearly blind, handicapping his ability to contribute and further marginalizing him from the group.