I am with Mek on this one, we drink because we like the feeling it produces. Here is what the AA Big Book 1st edition says about it:
Men and women drink essentially because they like the effect produced by alcohol.
Now non-alcoholics also drink for the same reasons, but the big book goes on to describe feelings and actions that are unique to us problem drinkers or alcoholics:
The sensation is so elusive that, while they admit it is injurious, they cannot after a time differentiate the true from the false. To them, their alcoholic life seems the only normal one. They are restless, irritable and discontented, unless they can again experience the sense of ease and comfort which comes at once by taking a few drinks-drinks which they see others taking with impunity. After they have succumbed to the desire again, as so many do, and the phenomenon of craving develops, they pass through the well-known stages of a spree, emerging remorseful, with a firm resolution not to drink again. This is repeated over and over, and unless this person can experience an entire psychic change there is very little hope of his recovery.
I know this was true in my case, and I even saw it coming back in my 20s. I unfortunately did nothing about it until I hit 44.