In the laboratory and in everyday situations, evil acts shape the self. People induced to harm an innocent victim typically come to disparage the victim. Those induced to speak or write statements about which they have misgivings will often come to accept their little lies. Saying becomes believing. Positive actions -- resisting temptation, giving help to someone, behaving in a friendly way in desegregated situations -- also shape he self. Evil actions corrupt, but repentant actions renew. In the words of the great 19th century educator Horace Bushnell, 'No truth is taught by words or learned by intellectual means ... Truth must be lived into meaning before it can be truly known.' In short, behavior impacts cognition more than cognition impacts behavior. (Perry W.H. Shaw, "Training to Failure, Training to Success: The Hidden Curriculum of Seminary Education")
Funny enough, my mind jumped to a scene from Batman Begins that I recently caught on TV. Pre-Batman Christian Bale is being induced to kill a farmer, someone whose wrongdoing he is not allowed to know. But in the "other-centered" (that being the group into which he would be inducted) nature of this killing, he would be embracing a way of life that looks good on the surface but already has the slight scent of sinister evil.
Bale seems to grasp this principle: that if he were to go along with the killing -- even if he didn't necessarily agree with it -- the evil would eventually overtake him. Instead, the reverse is true: he embraces a lifestyle of doing good, and eventually he comes to believe that what he is doing is right. (at least, that's my interpretation.)
"Truth must be lived into meaning before it can be truly known." - Horace Bushnell