Al-Anon is a well known 12-Step program that branched off from Alcoholics Anonymous. It, along with Alateen for adolescents, is a self-help group for the relatives and spouses of alcoholics. It considers the people who often live with Alcoholics and who either try to "fix" them or cover for and protect them to be "enablers" or "codependents."
Wikipedia defines co-dependency thusly: "It is a tendency to behave in overly passive or excessively caretaking ways that negatively impact one's relationships and quality of life. It also often involves putting one's needs at a lower priority than others while being excessively preoccupied with the needs of others." In a sense, the co-dependent is addicted to dealing with relatives and romantic partners who are themselves addicted to alcohol.
The alcoholic hides the bottle; the co-dependent finds it and tries to hide it somewhere else. In almost all cases, the bottle is somehow found anyway. (This is one of the limitations to studies that try to employ animal models of alcohol addiction. No one has ever been able to find rats who hide bottles).
Alanon's basic message can be summed up in one phrase, "Let go and let God." What this is supposed to mean is that co-dependents, like their alcoholics, are too willful. They wrongfully think that they should, and are powerful enough to, take responsibilty for the problem drinker. Hence, they need to "let go" of this need to be powerful, and surrender their will to a higher power. They need to "let go" and leave their alcoholic's problems for God to take care of, one way or another.
This is actually helpful advice, but not for the reasons advanced by 12 step programs. 12 step programs are based on Protestant techniques that are used to convert others to that religion. While there is psychology involved, it is a phenomenon that would be most appropriately studied by social psychologists, and sociologists, since it involves group dynamics.
On the surface, "Let go and let God" seems to be advice to not do anything about the alcoholic's self destructive behavior, but to leave it in other hands. The paradox, however, is that by not enabling, they are in fact doing something - something, in fact, that is completely different. As I described in my post, The Mother Teresa Paradox, if you constantly try to protect people from themselves, you interfere with their motivation for taking responsibility for themselves.
But it goes deeper than that. If you compulsively rescue alcoholics, then they and everyone around you will start to think that rescuing them is something you need to do. Why, if you did not have an alcoholic around, they tend to think, you would not know what to do with yourself. The alcoholic will not deprive you of this role, so he or she will continue to drink - just so you can keep performing it!
So, if you buy into the Alanon philosophy, and you quit trying to rescue the alcoholic, you take away his or her motivation to keep you "satisfied" in this peculiar way. Now of course this does not guarantee that the affected alcoholics will for sure stop drinking. They may decide to leave the relationship and find another enabler, or start destroying themselves without any help at all.
However, by changing their approach in this manner, the "co-dependent" is increasing the odds that his or her drinker will change for the better. By not doing something, they are doing something: employing one of the most effective interpersonal strategies that exist.