But Luther's question was not whether his sins were big or little, but whether they had been confessed. The great difficulty which he encountered was to be sure that everything had been recalled. He learned from experience the cleverness of memory in protecting the ego, and he was frightened when after six hours of confessing he could still go out and think of something else which had eluded his most conscientious scrutiny. Still more disconcerting was the discovery that some of man's misdemeanors are not even recognized, let alone remembered. Sinners often sin without compunction. Adam and Eve, after tasting of the fruit of the forbidden tree, when blithely for a walk in the cool of the day; and Jonah, after fleeing from the Lord's commission, slept soundly in the hold of the ship. Only when each was confronted by an accuser was there any consciousness of guilt. Frequently, too, when man is reproached he will still justify himself like Adam, who replied, "The woman whom thou gavest to be with me" – as if to say to God, "She tempted me; you gave her to me; you are to blame."
There is, according to Luther, something much more drastically wrong with man than any particular list of offenses which can be enumerated, confessed, and forgiven. The very nature of man is corrupt. The penitential system fails because it is directed to particular lapses.
-from Bainton's Here I Stand: a Life of Martin Luther, (Abingdon Press 1950, page 55)