The GAP is a key perspective in helping you decide who or what you are going to process. The idea here is to avoid comparing the person or situation with others (horizontally). There is always someone who has had it better or worse. If you compare horizontally, you will tend to minimize or make excuses for the offending person, and therefore never process the offense, hurt or loss.
By comparing your offender or situation with God’s character or design, you are “comparing up” (vertically) and taking the other person's motives, abilities and even how you have been affected (horizontally), totally out of the equation.