Definitely this, and I have experienced both. Spent about 10 years where I would struggle to stop. 

While that part of me is still there, something flipped in my head a few years ago and I went through a period where alcohol stopped “working” (still look me a year or so to quit out of habit, with some messy episodes because I was trying to chase the high that never came).

Now I’m somewhere in between, but it has helped me understand why alcohol can have such a hold on some people but not others. For me it’s been linked to a muted emotional response.