Something that was really groundbreaking for me was the realization that my resentments were about me, not about other people.
I found it really difficult to forgive other people, they wronged me, why should I forgive them? But really, the problem isn't forgiving them, it's forgiving myself.
I had a "friend" who used to pick on me a lot, he'd snicker at the things I said, the choices I made, he'd watch and remember unflattering, embarrassing things and kept track of them, and would bring them up later in front of other people to humiliate me. I hated him, or at least I thought I did, but really I hated myself.
The things that he said hurt me because I believed them to be true, he didn't plant those thoughts in my head, he just shed light on beliefs that were already there. I felt inadequate and inferior, and he reinforced that belief. If he called me a pink elephant I wouldn't care a single bit, because it's not something I believed or worried about.
What painful belief are you carrying around, that the doctor sheds light on?