Self-control operates much like a cybernetic feedback system and includes 3 interacting components: the setpoint, a discrepancy, and the correction (or reduction of discrepancy). In order to successfully exercise self-control, one must have a setpoint (where do I want to be: a goal), detect discrepancies between where am I now and the setpoint, and then have the ability to reduce or eliminate the discrepancy. Put simply: self-control requires a goal, an obstacle, and the ability to overcome the obstacle. Self-control training must target all three parts of the triad.
Of course, it’s more complicated than that. Everything is more complicated than a few sentences.
References: Michael Inzlicht, Lisa Legault, and Rimma Teper , Exploring the Mechanisms of Self-Control Improvement. Current Directions in Psychological Science 2014, Vol. 23(4) 302–307.
Cziko, Gary The Things We Do: Using the Insights of Bernard and Darwin to Understand the What, How and Why of Behavior, published by MIT Press 2000.