It's the old question of what suddenly makes the light turn on. In most cases, the light was always on, but wasn't or couldn't be observed. Alcohol distracts the drinker and dulls awareness of the situation.
The difference once someone quits and then observes the benefits they understand the danger. It's no different than someone texting and running in other lanes if they could see their actions from a third person view they would understand the danger. It's the same for jobs and professions, many people go to work unaware in a terrible mood, stressed, and wondering why the day wasn't good. If they could see themselves in a third-person view they might correlate as to why others are in a good mood.
I've always viewed it this way and it's a weird analogy but it works. A mouse or rat inside a maze isn't much better than being trapped in alcoholism. But once sober you see above the maze and understand which turns to make to escape.