There's nothing I've experienced in life that's as destructive as resentment. Nothing is as harmful, painful, or ultimately pointless. On a quick search, I've found several variations of a quote that's been attributed to several famous figures. Instead of researching and satisfying my curiosity about the original instance, I'll just paraphrase and let the glory fall to whomever it may:
"Not forgiving someone is like drinking poison and waiting for the other person to die."
How frustrating that, even knowing what I know about this subject, throughout my life I've always wrestled with forgiveness. Even now, I question things I've put behind me; wrongs done against me, fights I've had, fallings-out I've experienced. I sometimes revisit them in my mind, and I'm occasionally shocked at how tender the subjects still are. It's like I still bear the weight of these burdens, even years later.
I think all of this goes to show that time doesn't heal all things. It's like in the case of an actual flesh wound. Sometimes there are factors to consider; an infection, the venom of a sting or bite, or even just an increased severity can complicate that healing process. These can be seen as an allegory for things like a codependent relationship, a betrayal, or simply the termination of a deep bond. Proper care is needed, rather than just putting on a proverbial Band-Aid.
So often, my solutions to painful situations have involved cutting something or someone out of my life. The effect is essentially out of sight, out of mind. Of course a thing will stop hurting if it's taken out of focus, especially if there's other pain to replace it. And there always is.
What I'm trying (and slowly, finally succeeding) to find is the proper treatment for the condition of a bitter heart. We use terms like, "Give it to Jesus," as though it's as simple as physically handing Him an object. But when you have little or no experience with that, it just comes off as a Christianese platitude. On the other hand, when there's an action you can physically take, like doing something entirely for someone else, it provides an avenue for a real change in the condition.