One thing I forgot to mention in terms of "crossing the line." By that I mean that moment where the mental compulsion and physical craving to drink progress beyond the strict rational control of the individual. In other words, the individual can no longer predict when or how much he will drink, or what he will do if he does.
Also, the mental compulsion remains long after the body detoxifies. This is what the 12 Steps of AA try to treat, as well as a spiritual malady that some AA members believe exists.