The way I understand it is it is a mental disease, or at least a chemical imbalance in the brain. For some reason something turns your dopamine on in your brain, which is your "I gotta have it" chemical. When this happens we don't think rationally and until we get what we are after you will crave it. I just read a great book called "the Craving Brain", and it really made sense to why I crave alcohol, nicotine, food, sex etc. It also explains why programs like AA and SR work for people because these activities raise your serotonin levels that balance out the dopamine. I have always been taught that it was a self control issue, but I am a smart, well educated, successful person, who has a strong moral compass, but I could never understand why I would continue to seek out things that I knew were bad for my health and life. This book really explained it to me where I could understand why my brain craved things that I knew were bad.