לרפואת שרה לאה בת רבקה בתוך שח"י!!
There are numerous elements to teshuva. One is changing one's perspective about the sin. The act is a "done deal" but the RELATIONSHIP to the act, the ATTITUDE toward the act, the personal narrative about the act, can be changed. The primary aspects of a person are his thoughts, feelings and emotions so he can therefore retroactively undo the negative effects of his deed by showing that if he would have the opportunity to do this sin now - he would NOT do it. He can change his reality by making his act a מתעסק - an unwitting, unintended action.
But there is an additional aspect to teshuva: Many people afflict themselves in order to atone for their sins. How does that work? What is the rationale behind afflicting oneself for atonement? [I for example fast - when I am sleeping...]
We know from the gemara [Krisus 19b] that even a מתעסק is culpable in instances of חלבים and עריות. As we explained in the previous post - the sin of eating forbidden foods and forbidden relations is not the very act but the attendant pleasure involved - "שכן נהנה". So in order to counter and neutralize the pleasure of the sin, a person afflicts himself.
It should be noted that although regarding חלבים and עריות the sin is the pleasure while regarding other acts the sin is the act - there is still a sin for the pleasure. The more pleasurable the more sinful. The Chofetz Chaim says that if when one speaks lashon hara he lets out a krechtz ["groan" in Spanish] in his heart, then he has minimized the aveirah. So whenever you are doing something you shouldn't - at least feel badly as you are doing it.
So really ANY AVEIRAH can be partially atoned for by self-affliction and self-abnegation [I gotta take those SATS and see how I do. With words like "self-abnegation" I have a shot at doing OK].