Often an alcoholic will say, "I don't drink, because I know I am an alcoholic and the first drink does the damage."
This is what the Big Book has to say on the subject:
"Above all, he believed he had acquired such a profound knowledge of the inner workings of his mind and its hidden springs that relapse was unthinkable. Nevertheless, he was drunk in a short time. More baffling still, he could give himself no satisfactory explanation for his fall." (Page 26)
"He had much knowledge about himself as an alcoholic. Yet all reasons for not drinking were
easily pushed aside in favor of the foolish idea that he could take whiskey if only he mixed it with milk!" (Page 36)
"But the actual or potential alcoholic, with hardly any exception, will be absolutely unable to stop drinking on the basis of self-knowledge. This is a point we wish to emphasize and re-emphasize, to smash home upon our alcoholic readers as it has been revealed to us out of bitter experience." (Page 39)
"He was positive that this humiliating experience, plus the knowledge he had acquired, would keep him sober the rest of his life. Self-knowledge would fix it. We heard no more of Fred for a while. One day we were told that he was back in the hospital. This time he was quite shaky. He soon indicated he was anxious to see us. The story he told is most instructive, for here was a chap absolutely convinced he had to stop drinking, who had no excuse for drinking, who exhibited splendid judgment and determination in all his other concerns, yet was flat on his back nevertheless." (Page 40)
"I saw that will power and self-knowledge would not help in those strange mental blank spots." (Page 42)