In The Crucible, neighbors suddenly turn on each other and accuse people they've known for years of practicing witchcraft and devil-worship. The town of Salem falls into mass hysteria, a condition in which community-wide fear overwhelms logic and individual thought and ends up justifying its own existence. Fear feeds fear: in order to explain to itself why so many people are afraid, the community begins to believe that the fear must have legitimate origins.
In The Crucible, hysterical fear becomes an unconscious means of expressing the resentment and anger suppressed by strict Puritan society. Some citizens of Salem use the charge of witchcraft willfully and for personal gain, but most are genuinely overcome by the town's collective hysteria: they believe the devil is attacking Salem. And if the devil is attacking your town, then ensuring that your neighbor is punished for selling you a sick pig suddenly becomes a religious necessity, a righteous act that protects the God you love and proves that you're not a witch or a devil-worshipper. The Crucible shows how religious fervor fuels hysteria and leads to conditions that sacrifice justice and reason.