Popular culture encourages us to "think positive," yet research shows that merely indulging in positive future fantasies can undermine effort and achievement. How, then, can people pursue their desired outcomes without falling into the trap of wishful thinking? Mental contrasting, a self-regulation strategy that juxtaposes desired futures with critical obstacles that may impede them, offers an empirically-grounded answer. By activating nonconscious cognitive and motivational processes, mental contrasting helps individuals commit to feasible goals and disengage from unrealistic ones. Empirical evidence demonstrates its broad effectiveness: Sedentary men who were introduced to mental contrasting exercised more over seven months, students improved their eating habits, and diabetes patients managed daily challenges more effectively. When combined with implementation intentions ("if-then" plans), mental contrasting, now known as MCII or WOOP (Wish, Outcome, Obstacle, Plan), becomes particularly effective for overcoming impulsive barriers to behavior change. Teaching WOOP to chronic back-pain patients increased physical capacity, giving it to spousal caregivers of Alzheimer's patients reduced stress and depression and introducing it to stroke survivors enhanced exercise adherence and weight loss. Together, these findings show that WOOP is a simple, autonomous, and cost-effective mental strategy that strengthens self-regulation and promotes physical and mental well-being across diverse populations.