IV. Psychology of St. Augustine
With a spiritual orientation, Augustine's remorse for his previous lasciviousness was heightened by a harsh contrast with the strict carnal discipline of the ascetics, who were regarded as spiritual heroes.  Reading Augustine gives a picture of a man who was not at peace with his past, but was deeply disturbed by his earlier failure to control his "insatiable" sexual excesses. [79, 80] Augustine seems to have been afflicted with an incessant burden of neurotic guilt and self-loathing occasioned by his indulgence of a hyperactive libido. He suffered from scruples, regarding any pleasure derived from the senses as sinful -- even sacred music used in worship  -- and retrospectively viewed himself as a great sinner even as a child. 
Pagels observes that "what each of us perceives and acts upon as true has much to do with our situation, social, political, cultural, religious or philosophical."  To this list can be added our emotional situation.
Thought processes are influenced by emotions and thoughts colored by them. The Greek philosopher Porphyry, with whom Augustine was well versed, recognized that our reasoning is impeded from its proper operation by our bodily senses and the passions which they stir.  We cannot separate the functioning of the mind from the condition of the psyche. The output of an intellect, no matter how brilliant, will be distorted by emotional imbalance.
Simpson puts it more pointedly:
[R]easons are inseparable from the personality of the reasoner, whether they apply to his own behavior or that of others. They are grounded not in the situation in which the decisions are made, but in the reasoner's psychic definition of past experience, and that psychic definition frequently crosses all boundaries of rationality. Passionate irrationality in the name of impassioned reason occurs in the market, the classroom, and in science, as well as elsewhere, and often unconsciously. 
Augustine's theology could not but be distorted by his ponderous feelings of guilt. Augustine's consequent creation of "original sin" is analogous to the Genesis authors' creation of "the fall" -- a scapegoating device created subconsciously to lessen his own burden of guilt. (See Section VI below.) Indeed, in his Confessions, Augustine assumes the role of victim rather than perpetrator of his own sins:
I saw that when I acted against my wishes, I was passive rather than active; and this condition I judged to be not guilt but punishment. 
Augustine's empirical base of knowledge for his views was limited to himself. On the basis of his personal experience alone, he painted all of humanity with the brush he painted himself: guilty! From his deep-seated sense of personal guilt, he interpreted Scripture and created his theories of fallen human nature and hereditary punishment. He closed his mind to the validity of the contrary experience of others -- not only his opponent, Julian, but also his close friend, Alypius, who lived in total continence  -- and the concomitant invalidation of his universal generalizations. Nevertheless, for reasons that had much to do with the politics of authority in both the Church and the Roman Empire, Augustine's radical notions replaced traditional orthodoxy and became the law of the Church and the law of the land. 
But why would Augustine's pessimistic view of humanity receive such enduring acceptance? Pagels suggests that durability arises from the human tendency to accept blame for misfortunes beyond our control -- a seeming paradox in light of our common denial of personal wrongdoing. We would rather feel guilty than helpless in the face of disease, accidents, and natural disasters. Our psychological need to find reasons for such suffering is satisfied by Augustine's theory of original sin. In putting the blame for our suffering back on our first parents, "original sin" explains why we are punished without being personally at fault.