Sometimes people say, thanks to AA, they can now 'choose' not to drink.
A choice is a situation where one is presented with two or more options, and one must weigh up which to select.
Such options, however, must be reasonable, for the word 'choice' to be validly applied.
For instance, if you are weighing up whether to buy semi-skilled or skimmed milk at the supermarket, and you are largely content with both options, albeit preferring one over the other on this occasion, you can legitimately call this a choice.
If, however, you are asked to choose between confessing to a minor misdemeanour you did not commit and being shot, you technically have a choice, but pragmatically do you do not: the option you favour is actually a third one, namely not confessing and not being shot, but that option is not available to you. Any reasonable analysis of this situation would conclude you are being forced to confess. Your exercise of 'choice' is merely the recognition of a single viable (but unpalatable) option.
Another example: if one is given the 'choice' of reading a book or turning into a lobster, one must by necessity read the book, as turning into a lobster is not physically possible. Simply presenting multiple options and saying one has a choice does not mean one does. The options must be possible and reasonable for one to speak legitimately of choice.
If you are an untreated alcoholic, 'not drinking' or 'stopping at one' are, for you (unlike for normal people) like turning into a lobster: downright impossible. There is only one option (drink to excess), and thus there is no choice.
If you are sober, and your experience suggests that taking even one drink could trigger an unstoppable process that could lead to your death, having a single drink is not a genuine option, any more than hacking off your big toe with a butter knife or setting fire to your hair. The action could physically be taken and is thus more 'possible' than turning into a lobster, but it furthers no purpose, causes harm, and runs so counter to one's being that, pragmatically speaking, it is not in reality any more viable than turning into a lobster.
The transition is this: having one viable option, namely to drink, to having one viable option, namely to stay sober.
On those rare occasions when one has to 'think it through' or genuinely weigh up the pros and cons, and 'chooses' sobriety over drunkenness, the truth is this: you are partly insane, but fortunately more sane than insane, so the sane thought wins. This is not the exercise of choice; this is winning on a balance of probabilities.