Many people get quite excited about forgiveness at first and just dive into practicing it, only to lose interest after a few months. They literally just let it fade from their minds and hearts as they go on to the next popular diversion in life. In other words, they do not have a strong will to keep forgiveness before them as a practice and as a way of seeing the world.
This could happen to you. A commitment to forgive does not just mean a short-term commitment toward one person who has hurt you in one particular way. Commitment has a must longer reach than this. Would you become physically fit if you worked out several times a week for three months and then hung it all up? Of course not. It is the same with forgiveness. You have to fight against the tendency to just let it fade in you. You will have to fight against all of the distractions of life that call you away from it.