This paper provides a framework for analyzing the dynamics of self-control. Making a decision brings not only material utilities but also a mental cost. The mental cost is determined by the strengths of automatic processes which impose initial evaluations of utilities and by the proficiency in employing controlled processes to temporarily modify the evaluations. Repeated exertion of self-control weakens the automatic processes toward the instant rewards and strengthens the automatic processes toward the delayed punishments, which results in “momentum” in self-control behaviors. Two approaches of intervention are analyzed. Avoiding the cues can keep the decision-maker from the harms of the tempting choice but cannot enhance his self-control ability. External incentives can help weaken the automatic processes toward the instant reward, but they crowd out the strengthening of the automatic processes toward the delayed punishments. Thus my model predicts that it will be more effective to provide a lower external incentive but still sufficient to induce subjects to resist the temptation, in the sense that they are more likely to resist the tempting choice after the treatment than those who are provided with higher incentives.