Our first parents fell into open disobedience because already they were secretly corrupted; for the evil act had never been done had not an evil will preceded it. And what is the origin of our evil will but pride? For “pride is the beginning of sin.” And what is pride but the craving for undue exaltation? And this is undue exaltation, when the soul abandons Him to whom it ought to cleave as its end, and becomes a kind of end to itself. This happens when it becomes its own satisfaction….The devil, then, would not have ensnared man in the open and manifest sin of doing what God had forbidden, had man not already begun to live for himself….By craving to be more, man became less; and by aspiring to be self-sufficing, he fell away from him who truly suffices him.
–Augustine, The City of God 14.13