Rarely have we seen a person fail who has thoroughly followed our path. Those who do not recover are people who cannot or will not completely give themselves to this simple program, usually men and women who are constitutionally incapable of being honest with themselves. There are such unfortunates. They are not at fault; they seem to have been born that way. They are naturally incapable of grasping and developing a manner of living which demands rigorous honesty. Their chances are less than average. There are those, too, who suffer from grave emotional and mental disorders but many of them do recover if they have the capacity to be honest.
From Chapter 5, pages 58-60
of the Big Book of Alcoholics Anonymous