The impulse to drink arises.
It is sent to the Command and Control Centre (CACC).
It is powerful.
The CACC normally assesses the pros and cons of ideas.
With the impulse to drink:
(1) The CACC is knocked out altogether or
(2) The CACC activates but cannot see straight: reasoning 'concludes' a drink is safe or
(3) The CACC activates and realises the truth but the impulse effects a manual override
In all three cases, the impulse converts into action: a drink.
From the Big Book (the only three references in the basic text):
There is the obsession that somehow, someday, they will beat the game.
The idea that somehow, someday he will control and enjoy his drinking is the great obsession of every abnormal drinker.
There was an insistent yearning to enjoy life as we once did and a heart-breaking obsession that some new miracle of control would enable us to do it.
The obsession, thus, is not preoccupation in the sense of constantly thinking about alcohol but the persistent delusion that to drink is safe.