He and Bob each had tried to get sober independently, but to no avail. Then they met.
Bob had this to say about their meeting:
[Bill] gave me information about the subject of alcoholism which was undoubtedly helpful. Of far more importance was the fact that he was the first living human with whom I had ever talked, who knew what he was talking about in regard to alcoholism from actual experience. In other words, he talked my language. He knew all the answers, and certainly not because he had picked them up in his reading. [Italics in the original] —Alcoholics Anonymous, third edition, p. 180
This nugget, tucked into the doctor's story like a hidden gem, is perhaps subliminal acknowledgement of the key to his long sought freedom from drink.   
—Alcoholics Anonymous, third edition, p. 180

Bill never took another drink, and after one final fling on June 10, 1935, Bob never had another drink either. Following what has become the core of the AA program—meetings—millions of alcoholics have found long term sobriety. Many believe that a belief in a higher power has helped them achieve sobriety, and many who have found themselves unable to believe in a higher power have also been able to achieve sobriety by meeting with other alcoholics who also seek sobriety. It is salutary that AA started when two alcoholics who had both tried to get—and stay—sober were only able to get sober after meeting—and working toward sobriety together. The conclusion we draw from this is that the talking of one alcoholic with another about their common problem and their common aspiration is of paramount importance for AA. This conversation, many of us believe, is the true source of AA's power.

In 1957 Bill wrote in
Alcoholics Anonymous Comes of Age:
“...this was the great contribution of our atheists and agnostics. They had widened our gateway so that all who suffer might pass through, regardless of their belief or lack of belief.” (p. 167)