I've read that scientists are discovering types of genes which cause addiction by stimulation of dopamine receptors, triggered by the first few drinks a person ever has. (In fact, any substance or activity which releases dopamine becomes the trigger if one has inherited these genes or parts of a gene, so it could include gambling, drugs, nicotine, even sex) The brain drives the person's desire to repeat the pleasure rush, and the addiction is engendered. People without this genetic structure can experience the pleasure, but are not driven to keep it going by repeatedly, say, imbibing alcohol. It would seem from this that personality,life experiences etc have less to do with addiction than one's genetic make-up.