You must do exactly what you committed to do. A well formed commitment is developed with the no-exceptions requirement in mind, and so requires a clear specification. Motivation changes with local conditions. In the beginning, addicted individuals are highly motivated to adhere to their decision to change. As the crisis that motivated the commitment recedes into the past and one becomes involved in the continuous stream of events that play out in real time, the commitment decays.
Local motivation becomes more a function of local circumstances than the distant commitment.
The motivation to maintain abstinence is greater during the contrite state following an unfortunate drinking episode, than during a high risk situation some months later. Motivation is an abstract construct, but action changes the world. Whatever happens at the moment becomes part of the performer's biography. I am a psychologist, and people generally seek my services because they have relapsed - regained the weight they lost, gone back to drinking or drug using, etc. Oddly, they don't know.