Naturally, it is different for every individual to a certain degree. I feel that you can pretty much compartmentalize every alcoholic into a small number of variables.
Me personally, it was a predisposition with some environmental impact and self-medication (from an unstable child-hood, divorce parents). I drank beer, smoked weed and as I matured those indulgences eventually went away.
The first time I drank liquor, which was a Martini, it tripped a breaker in me neurologically.
When we bought our house, that was the environmental aspect. It allowed me the comfort of drinking at my own disposal.
I don't accept anything without knowing the details behind it.
I naturally gravitate to finding comfort in details. I've followed the breadcrumbs and I've come to the conclusion on how I became and alcoholic.