To get forgiveness you have to show genuine remorse and a commitment to change behavior. Forgiving people who don't own the harm they cause is like letting them off the hook to harm someone else. Repentance and forgiveness go together. I would never refuse forgiveness to someone who sincerely asked for it. I would never forgive someone who was likely to repeat the harm to someone else because I didn't insist on their change.

Having said that, some slights are just not worth holding on to. If someone cuts me in line or a driver is rude...let it go. When real harm has been done, I want a genuine expression of true remorse.