It's common for people suffering with an addiction to tell others, or even themselves, "I promise I'll stop (my addictive behavior)" or, "I commit to stopping." This isn't surprising, since having an addiction generally means feeling out of control and leads people to the idea that they should finally take a stand to regain control of their lives. Those around them are also often desperate to hear precisely this commitment from them. And people with addictions commonly feel guilt for causing distress to family and friends and want to reassure them, even when they aren't actually clear whether they can keep that commitment. In fact, folks suffering with addictions may know perfectly well that they aren't telling the truth when they promise to stop, but feel it's best to avoid a useless fight. Besides, they may hope that, even though they'll continue the behavior, they can keep it a secret.
But in almost every case, making a promise to stop is a recipe for harm. With any action driven by a powerful psychological need, such as every compulsion or addiction, promises and commitments to stop nearly always fail. Then, very bad things happen. Those who made the promise feel worse about themselves. Their loved ones feel worse about them, seeing them as untrustworthy, or even unloving ("If he loved me, he would keep his promise"). Everybody becomes angry with the person who "broke his word," and even more tragic, everybody becomes more discouraged. This can lead to more impossible-to-keep promises, or to precipitous and poorly-thought-through changes in treatment plans, such as suddenly pulling people out of otherwise good outpatient therapy, or sending them away to expensive and nearly always useless rehabilitation treatments ("He can't be trusted so he needs to be locked up").
The reason promises fail is simple. They are based on the idea that addiction is a question of willpower. Saying that one commits himself to not performing an addictive act is the same as saying he will use all his willpower to not do it. But, as anyone suffering with addiction, or anyone familiar with this blog or any of my books knows, the drive behind addiction is entirely independent of willpower. Indeed, it is just the opposite. Addictive behavior is driven by psychological factors that are completely separate from conscious willpower. These factors can certainly be understood and managed, but as with all other emotional symptoms, the behavior is not generally manageable by simply deciding not to do it, no matter how hard you try.
Sadly, there are some therapists (and many rehab centers) who fall into the trap of urging their patients to commit to stopping their addictive behavior. Sometimes, they even urge that people make a commitment to them, the therapists! Not only does this reflect a failure to understand the nature of addiction, and not only does this lead to all the problems I mentioned above, but when the commitment fails, the treatment is in trouble. Having been based on a false premise that promising the therapist could stop the behavior, the treatment is now groundless. The right way to treat people in psychotherapy is to help them to see exactly what predictable emotional issues lead them to feel overwhelmingly helpless, which lead directly to their addictive urges (my second book, Breaking Addiction, is devoted to describing just how this works).
If you suffer with an addiction, then, the first step is to think through whether you really intend to stop, or not. If you don't intend to stop, then you won't until you revise that view. But if you decide it's your intention to stop, you will be in a good position to deal with any future slips, since you won't be confused by rationalizations about why you slipped. You won't be confused by the rationalization that "this time was different" because you already declared your intent to stop altogether, no matter what.
Deciding that you intend to stop is very helpful, but that is very different from making a promise to stop, to yourself or others. Being clear that it is your intention to stop is essentially just making a plan for yourself. It's a very good plan. But making it does not guarantee success, and failing to perfectly carry it out is neither shameful nor a reason to give up. That's why the plan should never be a promise. It is critical that both the person with addiction and those around him or her understand this.
If you have an addiction, then, get into a good therapy to find out why, and therefore when, you will have addictive urges. You can then truly reassure your loved ones— that you are going to work at the therapy as well as you can. Remind them that "slips"— brief resumptions of addictive behavior—are the norm and not a cause for panic or discouragement.
If you are the loved one of someone with an addiction, help that person to get into a genuine psychotherapy to understand what precipitates his behavior, and don't pressure him or her to promise anything about his addictive behavior. I realize this advice isn't easy to follow when you are worried and would like nothing better than to be reassured. But if you can keep from expecting this, both you and your loved one will be spared a lot of unnecessary pain.