Augustine of Hippo

And indeed pride, although it be in itself a great sin, is of such sort in itself alone apart from others, that it for the most part follows after and steals with more rapid foot, not so much upon sins as upon things which are actually well done. However, that which he has understood in another sense, is after all most truly said: "Pride is the commencement of all sin;" because it was this which overthrew the devil, from whom arose the origin of sin; and afterwards, when his malice and envy pursued man, who was yet standing in his uprightness, it subverted him in the same way in which he himself fell. For the serpent, in fact, only sought for the door of pride whereby to enter when he said, "Ye shall be as gods." Truly then is it said, "Pride is the commencement of all sin;" and, "The beginning of pride is when a man departeth from God."