We're taught from an early age that we must do what’s right even if others don't. Karma teaches us that we’re accountable for ourselves and accountable to others too, therefore it is important we do what's right, even if others fail to do right by us.
Doing what is right is about trust. When someone puts their trust in us and we let them down, it says more about us, than it does about the person we let down. If we let someone down, it is important we go back in, correct what we've done.
Even if we don't do what's right and choose to move on, we must always go back in and right a wrong. As karma dictates it's the right thing to do. Life also works out better for us when we do.