There are many interesting pieces of research about genetic and environmental factors in addiction. Here's a typical instance...

I'm personally of the opinion that a complex genetic makeup gives rise to people with a predisposition to addiction, one which makes itself shown through particular social and environmental circumstances.

I smoked for several years as a young man but, when I decided to stop, had no problem in doing so - stopped overnight and stayed stopped - about 40 years ago. I enjoy beer and wine but I know that, if the doctor said, "No more alcohol for you", I would be able to stop immediately in a similar way. I don't think is so much willpower as a precondition in me to resist addiction - but who knows...?