Willpower is the ability to override one behavior in favor of another. Willpower often involves restraining impulses, overcoming inertia or resisting temptations Willpower is goal-directed; that is, it is exercised in the service of some goal. Low motivation or goal commitment undermines willpower - as does uncertainty about one’s ability to achieve a goal or uncertainty about one’s ability to exercise willpower.
When we try to resist temptations, there's a tension between immediate, certain reward and later, uncertain reward. The more certain the later reward, the more likely temptations will be resisted. But certainty is just one part of the equation. Later rewards may feel far-off, abstract, and only intermittently compelling, while temptations are concrete and immediately satisfying.
It’s good to periodically revisit goals to reconfirm commitment to them – but be careful not to overthink your goal decisions. (Is this what I really want? Why? What am I missing if I stay committed to this goal? Let’s go over the Pros and Cons again.) Overthinking about goals can undermine them too – and in the process, undermine the willpower needed to achieve them.
In response to temptations, develop quick and dirty “if/then plans” for dealing with them: if or when I encounter a specific temptation, do this. If there’s a plate of cookies, walk away from them. If someone offers me a cookie, say ‘no thanks’.
If goal commitment waivers while being tempted, use simple heuristics to resist the temptation – like “If I give in now, I’ll feel bad later”. The desire to avoid future regrets packs an emotional punch that makes it a handy willpower tool in the moment. Later you can think things over.