Rationalization is adjusting your ideals to match your conduct; Repentance is elevating your conduct to match your ideals.
When I was growing up I spoke to my Bishop about a certain situation and I was incredibly offended when I realized that he shared information about this situation with other members of our congregation. It took me a while to trust in church leaders after that.
After college I moved home and encountered this same church leader and he apologized for betraying my trust years prior. I hadn't ever confronted him or acknowledged that I knew he had irresponsibly shared my secrets. He knew he had and he apologized....repentance.
Same guy, same summer- I discussed a certain sin with him that I felt remorseful of. He expressed confusion and disgust because he had never heard of someone doing that before (awesome). I rebounded from that much easier as I had already well recognized that mankind is imperfect.
Recently, on a trip home to visit my parents, the man apologized for the more recent inappropriate comments he made to my about my behavior. He expressed sorrow and remorse for his lack of understanding and support....repentance.
I had nearly forgotten of the incident and was certainly not dwelling on it by that point. I will however, always remember his example of humility and kindness each time he said or did something incredibly inappropriate.
Repentance...ushering in hope