Best explanation I ever heard was from a guy at the Bouldin group, hell, had to be 35 years ago. He said early in his drinking career, he had that one drunk where everything seemed perfect. He felt great. He felt alive. And he spent the rest of his drinking career trying to recapture that feeling. I don't really buy the childhood trauma thing. I drank because I liked getting drunk. I liked the feeling of euphoria. Never understood how someone could leave half a beer.
It was never a problem for me to go a week or a month without a drink. When I started drinking, though, I didn't stop until I was stinking drunk. For a while I tried to convince myself I could have a few and stop when I got the right level of buzz, but nah. It's not a problem for me not to drink, so I'm more fortunate than many. If I ever say, "oh, I'll have one glass of wine," though, yeah, empty bottle and I wake up a half hour late for work.