I'm not sure I understand your question, lastchance. Sorry. I don't know if alcoholism can make the alcoholic "forget" the reason they quit, but it can certainly make us minimize the problem or make us rationalize drinking again...no matter how bad it got.
The decision to quit has to be carved in stone. No waivering. While there was probably a reason we all quit, our quitting cannot be contingent on that reason because we all know how our addiction can trick us into thinking the reason wasn't good enough.
I tell myself that my decision to quit was made during a moment of mental clarity. Anything else I tell myself about resuming drinking is the insanity of the disease.