I have had people apologize to me (sometimes repeatedly) for things that didn’t bother me at all. I have found some people’s offenses very easy to forgive, whether asked or not. And there are some that I don’t forget and never will.
If I consider these differences analytically, I think that in the first two instances my response mostly depends on how I felt about the person in the first place.
—A person toward whom I have a very strong, deep loving feeling is easy to forgive.
—A person toward whom I have weak or mixed feelings easily loses my regard. An offense is much less forgivable. It’s as if I were seizing on a reason to push them away. Those would perhaps be what you are calling grudges. I will probably keep my distance forever.
—A person toward whom I have no feelings or negative feelings pretty much can’t offend me or injure me because I simply don’t care what they think. But I will remember intentional wrongs committed, such as deliberate lies.
Thinking even more carefully, I believe that there’s a relationship to how I think the person feels about me. If I am secure in their affection, I tend to regard the affront as a harmless or at least human and forgivable mistake. If I am not, I think it means they do not think well of me, and then I want to remove them from my sphere of affection.
On the whole I would say I have become more forgiving with age, but there are some people to whom I will never expose any vulnerable part of myself for any reason and to whom I would not even give away trivial bits of information, such as in casual conversation. My mode of punishing is withholding.
Sometimes the actual offense is seemingly a trivial thing, on the surface, and that’s what makes it seem like a foolish grudge. But it can stand for a lot.
The big, important category of offense is betrayal of trust. Trust once lost must be earned back, and it is very hard to do. Self-protection says not to trust again. But I would still rather trust and be wrong than to withhold trust that I should have given. This is an area of unresolved conflict.