If you are fantasizing about relapsing, remember the endurance it took to be a practicing addict. The physical struggle, the lying, the financial losses, the relationship losses, the day to day depression, the painful cravings, etc. The fight to continue using never seemed to end even though life just got worse and worse. If you are tempted to pick up the first drink, drug, or illicit behavior, remember you don't want to even risk fighting again for a life of failure.
Think for a minute about how much easier and simpler life is without using.