One point on the whole negative/positive thing is that you can use a negative in a positive way. For example if you visualize the living hell of alcohol withdrawal whenever the slightest thought of drinking pops up it will put a buffer on the drinking thoughts.
I also wonder if some people just don't get caught up in a negative feedback loop when it comes to rehab. Think about it this way, a person goes to a rehab through family or work related pressure, (a negative), the rehab tells them they have to give up their only source of relief, (another negative), upon release the addict is informed that they must attend meetings forever and a day, (a very big negative, unless your the type of person that wants to go to meetings).
So now the addict is faced with the option of jumping into the circle of negatives or returning to his addiction (which he views as a positive). Could this be why so many fail?
Also there is a very big difference once someone has reached the end of their rope with addiction. I had reached the point where if someone told me that I had to paint myself hot flamingo pink and go for a naked 10 mile jog everyday I probably would have given it a shot. Age, maturity and how far you are in the progression are very big factors. In my 20's I don't know if there was anything that would have made me stop.