Miller tells us that initially, Hale "conceives of himself much as a young doctor on his first call...he feels himself allied with the best minds of Europe - kings, philosophers, scientists, and ecclesiasts of all churches." He shows up on the scene with loads of books believing that "the Devil is precise" and can be calculated, detected, and crushed. He believes he has successfully found witches in other places, and is now an expert.
As more and more people are accused, he states he trusts in God and the justice of the court to free those who are not guilty. But when he hears Giles and Proctor defending their wives, Hale himself begins to question the court. Unlike the judges, Hale sees the sense in the evidence being presented. Proctor's condemnation at the end of Act Three finally causes him to snap and realize the insanity of the proceedings.
Hale is humbled by this realization and spends Act Four trying to make up for his wrongs by getting prisoners to confess. He admits to Elizabeth that he had come into the village with confidence and from that time everything he had touched died. He feels responsible for the lives that have been condemned.