Memory: When I Have Been Wronged (Matthew 18:21-35)

In our 3rd lesson exploring how Christians should handle Memory, we consider the memories of the times we have been wronged by others. We first consider 6 possible responses to sin against us, all of them chaining us to the memory. So we then consider another way - the way of forgiveness. If this is God's intention for my handling of these memories, what makes forgiveness possible? What is my strategy?