Mr. Hale can be called cocky because he is so incredibly sure of himself when he arrives in Salem. When speaking of his religious books, he says that "they are weighted with authority" and that they contain the following:
All the invisible world, caught defined, and calculated. In these books the Devil stands stripped of all his brute disguises. Have no fear now—we shall find him out if he has come among us and I mean to crush him utterly if he has shown his face!
He speaks of the Devil as though the Devil is an easy and knowable adversary, as though he has the authoritative texts that will make it simple to identify and eradicate the archfiend who waged war on God. In Hale's mind, "The Devil is precise; the marks of his presence are definite as stone." This belief underwrites his confidence because he thinks that he knows all of these signs. For this reason, he has supreme confidence in his own ability to root out and defeat the Devil, and he has no doubt, no fear—he does not even seem remotely concerned that the Devil could trick him or that something unexpected could happen. He considers himself to be a part of an enlightened and elite group:
Allied with the best minds of Europe—kings, philosophers, scientists, and ecclesiasts of all churches.
Hale is exceedingly confident that defeating the Devil will be simple for him with his "weighty" books and trove of knowledge, and, frankly, his cockiness leads him to miss key signs of deception and corruption.