Sorry, Lotus, I'll just have to try and do better next time...
I believe that both the forgiving and the unforgiving personality are coming from the same emotional place, namely fear.
The one who forgives too easily and quickly tends towards people-pleasing and is often afraid of the conflict that ensues if they are completely honest about where they are (that would be me).
The unforgiving one is coming from a fear of being hurt (again) and their defense against that is to hold on to the hurt; if they forgive, then it feels too vulnerable and scary to let go (that would be my W).
As a "forgiving" type, I am learning to slow things down and process my own feelings more deeply before forgiving; as the "unforgiving" one, my W is learning to delve into her hurts, to express them, and ultimately forgive. I used to be "here, let me help you with that" - the effects of which are amusing in retrospect, but were rather painful at the time. Needless to say, I am learning to allow her to proceed at her (not my) pace.
Forgiveness is like exercising - it is very difficult to start with a huge weight or by running a marathon. One useful thing is to pick one (and only one) thing each day that my W has done that has annoyed me and forgive her for that. That is, to unconditionally release any negative thoughts I have. She (presumably) does the same.
It's sometimes an uphill struggle even with "small" things. The other night she was annoyed with something a friend of our son's did and was venting to me. I was trying to listen mindfully and validate her when something I said triggered her. She was upset and was yelling at me - and nothing I could do or say seemed to have any effect. I in turn got mad at her for misunderstanding my words. We wound up not speaking for the rest of the evening and went to bed mad. (Yeah, I know we're supposed to "never go to bed mad" - doesn't always work out that way!).
The next morning, I did some soul-searching and recognized that even though I had done nothing "wrong" to "deserve" her reaction, I had reacted to her reaction with a kind of holier-than-thou attitude. I then realized that her reaction was coming from her "old tapes" from the past, and really had nothing to do with me. So I forgave myself for my attitude that contributed to the conflict, and forgave her for her reactivity. Although we haven't discussed it yet, just that shift in attitude with forgiveness (which she likely has done as well) has made all the difference in how we have been since. In the past, even such a minor thing like this would have led to days of the "silent treatment."
The point being that the forgiveness "muscle" can be built up by starting with small things and moving to the bigger things.
Saffie, you are entirely right about not forcing it - the choice of forgiveness must be completely of one's own free will and (ideally) after having processed and acknowledged the hurt.