The Vicious Cycle
Anyone who has struggled with an addiction, or who knows someone who has, is likely to recognize the potentially disastrous cycle that can be triggered by stress and stimuli both internal and external.
The pattern usually proceeds thus. A person in recovery (though this can apply to a person currently using a substance) experiences some kind of trigger related to their substance, or even a general trigger in their life. This spurs thoughts of using (whatever substance, or acting out whatever behavior, etc) and then, usually, a struggle ensues in the mind and body of that person until the craving is either given in to or vanquished...for that moment.
It's easy to picture these things in terms of the popular imagination of addicts and addiction, which is people busted down to the street corner, shooting heroin in the gutter. It's much less comfortable for most people to see these things happening in their own life.
Types of addiction
Just as every person is different, so too is every experience of addiction. The popular conception of "rock bottom" and a life out of control elides the truth of addiction as a spectrum. Addiction can be a state of mind as much as a habit centered around a specific thing, and it can poison an otherwise healthy person even without the help of a substance.
One of the more interesting types of addiction is process addiction, also known as behavioral addiction. This is an addiction to an activity or set of activities. Often seen around video games (I have this problem myself) because they are designed to short-circuit the reward and pleasure centers of our brains, process addictions exhibit the negative consequences of substance addiction without the substance. Though the diagnostic tools for behavioral/process addictions have been slow in coming, they offer a way out of the addict/non addict binary that contemporary debate often seems locked into.
Behavioral addictions stimulate the dopamine reward system in the brain, in effect turning the mind itself into an addictive substance. When we conceptualize addiction as a set of learned behaviors with a chemical component, rather than a moral failure in an individual person, it not only lowers some of the stigma around acknowledgment and treatment but opens the possibility that the effects of addiction on ordinary people's lives will become open for discussion.