If you want to make a difficult behaviour change, forget about will power and try making a rule instead.
I just finished reading The End of Overeating: Taking Control of the Insatiable American Appetite by David A. Kessler, a book about the psychology and physiology of compulsive eating and the role of the food industry. In the 'self-help for overeaters' section, the author recommends that, rather than counting on will power, overeaters should implement strict and absolute rules to eliminate struggle when faced with foods that trigger overeating. According to Dr. Kessler, absolute rules eliminate the need for will power! Here's why: Will power is invoked in the moment. The second you're faced with a desired stimulus (let's say cake, but it could also be a desirable but unnecessary purchase, or reading your favourite news sites and blogs rather than starting to work in the morning), will power pits the force of your desire for the reward (food, purchase, Internet) against the force of your determination to resist, creating discomfort.
In contrast, a rule is a long-term principle created in advance and not in the presence of the desired/rewarding stimulus. A rule (e.g., "No dessert") is based on experience and on a rationale (e.g., that much sugar makes my heart race and gives me a sugar hangover the next day; I want to maintain my weight; I know if I have one piece, I'll end up having seconds and thirds) that allows you to inhibit your normal behaviour (see cake, eat cake), without struggle ("I want it--no, I shouldn't have any--but it's a party and I deserve it--but what about my weight--okay, maybe a small piece"). Having an absolute and completely integrated rule allows you to avoid the impossible task of remembering your rationale at the moment you're faced with the desired stimulus--the rule is so internalized that it's a given.
A budget rule is another example: say you and your partner decide that travel is one of your most important values, and that in order to save money to travel, your rule is to never eat out when you're in town. When you receive an invitation to go out for dinner, you don't debate or agonize or argue over it, because the decision is pre-made: you're not going. No struggle and no will power necessary!
The distinction between rules and will power caught my attention because this year, I stopped eating grains--no pasta, bread, rice, and no most desserts--and have been training (running) harder than ever before. Observing me decline brownies and skip social occasions to go for long training runs, a few people have commented on my will power. This comment makes me feel uncomfortable because it rings untrue: if I have so much will power, why don't I stop eating family-sized bags of Nibs in one sitting, repeatedly interrupting my work to check my email, and scratching mosquito bites until they become scars?
The concept of rules provides an explanation: I am following two completely integrated and internalized rules: 1) No grains; 2) The training schedule is law. These rules are congruent with the definition provided by Dr. Kessler: both were created in advance (in January and years ago, respectively), for rational personal reasons (related to physical and mental health) based on my experience and consistent with my long-term goals, and they allow me to inhibit my default behaviour (i.e., eat any and all available baked goods; sleep in/prioritize social life). So when I turn down a fresh cinnamon bun, it's not because I have will power (which implies that I struggled with the decision), it's that my rule dictates that cinnamon buns aren't even an option. Same with following my training schedule: I don't struggle over getting up early or skipping your party to run; it's not hard and it doesn't involve will power. (Think about vegetarians who used to enjoy meat. I don't think they struggle every time someone offers them a burger; they're just following their very integrated rule.)
I think what might take will power is the initial creation of the rule--making the rule and sticking to it until it becomes entirely integrated. The two rules above are the only ones I've succeeded in internalizing to the point that there's no struggle. Among myriad others, I've tried "11pm is bedtime," and "no email checking until lunchtime" without success.
NB: The use of absolute rules isn't entirely positive, and rules aren't for everyone. I think they may be more helpful for abstainers (people who are successful with a 'cold turkey' or all-or-nothing approach) than for moderators (people who can successfully indulge moderately or occasionally). (Read about this distinction here.) Further, the inherently rigid nature of rules can create problems (e.g., following your training schedule to the letter even when you're injured; following your no-dinners-out rule even when it's your best friend's milestone birthday party).
What are your rules? Do they work?