I'm not really talking about trauma or anxiety. I'm talking about a feeling of resentment and anger directed at the other - the kindling for that flame of anger

I'm not really talking about trauma or anxiety. I'm talking about a feeling of resentment and anger directed at the other - the kindling for that flame of anger is past injustice. Letting go of this is forgiveness, I think. It's specifically the injustice, rather than the hurt, that is keeps resentment alive. "It's not fair!" is the rallying cry. Hurt heals and lessens with time. But feelings can be nursed, indulged, prolonged, and inflamed. Understanding operates on a different plane to emotions. Intellectually you can understand why something happened, but that doesn't necessarily have an effect on your emotions. Emotions seem to have a life of their own, if you don't take responsibility for them. And of course that's a key part of growing up, of maturity: emotional regulation. You might use intellectual understanding as a rationale for regulating feelings of resentment, but it's neither necessary nor sufficient. You do need an act of will to let resentment go. And I think this is the core of forgiveness.