If you have some plan to undo the injustice, that's one thing. But if you are suffering for several generations in a futile attempt to undo the injustice, perhaps it's time to give up and pursue some other goals.
Aside: in the case of land disputes, how did the "victims" come about the land in the first place? Even if they were truly the first humans there, does that give them some divine right to it? And what about nomads?