We are creatures who have an intrinsic need for justice. We feel better when we see people who have wronged 'get what they deserved.' And yet, in this portion of Jesus teaching us how to pray, he makes it clear that his desire is for forgiveness, not restitution. In doing so, he makes a cry for injustice - both in terms of what we deserve AND what others deserve from us.
It may sound nice, but when the rubber hits the road and we think of actual people who have hurt us, forgiveness and injustice become much more difficult to live out. But it is how Jesus taught us how to live and it is what Kingdom living is all about.