You have to realize that whether the wrong was deserved or not, it’s an issue that you have to chalk up to karma. It doesn’t seem right that something you’ve forgotten so long ago should come back and hit you, but that’s how karma works.

"In terms of distress with reference to the world, the number one issue that’s hardest to put down is the sense that you’ve been wronged. There’s a very strong sense of self that grows around that and a very strong sense that if you don’t keep that in mind, you’re going to miss out on some justice, so you’re the one who has to keep the issue alive. You have to realize that whether the wrong was deserved or not, it’s an issue that you have to chalk up to karma. You may have done something like that a long time ago. It’s so long ago that you’ve forgotten and it doesn’t seem right that something you’ve forgotten so long ago should come back and hit you, but that’s how karma works. Sometimes things take many lifetimes before they show up. So it’s not a case of whether you deserved it or didn’t deserve it. It’s simply that there was a cause and this was the result. And there’s no need to feel that you have to keep it in mind in order to have justice done, because again, karma will work out. You don’t have to keep score. You don’t have to be the avenging angel.

So if thoughts come up of times when you’ve been wronged, just say, “Well, that’s karma. That’s the world. But it’s not my territory right now.” Remember the Buddha’s image of the quail or his image of the monkeys. When the quail goes wandering off out of its safe territory, it gets caught by the hawk. When the monkeys go wandering off out of their safe territory, they get trapped by hunters. As you go wandering off into things like that, you’re going to get trapped. Greed, aversion, and delusion are going to come get you. So remind yourself that your safe place is with the breath, and even though nothing much may be happening with the breath, at least you’re safe. Why go venturing out into dangerous territory? “Well, it’s more interesting,” you may say. Or again, there’s a sense of obligation. You think that certain thoughts have to be maintained in order to get justice done. Well, that’s wrong mindfulness."

~ Thanissaro Bhikkhu "Greed & Distress with Reference to the World"