Some people can "flip a switch"- they were addicted out of boredom -it was something to do or was an interesting vibe at the time, and they've since found something more fulfilling or satisfying.
Some people replace one addiction with another. They're living for the dopamine hit or the adrenaline rush, no matter what. Also, they tend to be the "it's not my fault, it's the drug, or alcohol, or whatever".
Some people are addicted because they're self-medicating. Those people are often harder to reach, because not only has their brain chemistry betrayed them, they realize it and are living with shame and uncertainty of their condition.
Because seeking mental health is considered a moral failing in Western societies, especially in the US, and the way we treat mental illness has a lot of force the patient to take more responsibility for their quirks or failings than one would the average functioning person.
The drugs and treatments are supposed to make you normal, however, because you're on treatment, you're not supposed to have a bad day, or mess up. A patient in treatment is under more compliance stress than someone who self-medicates.
And many times, that stress to comply ("you're better now, why can't you just...." ) - or the casual way insurance or pharmaceutical companies treat psychotropics, randomly denying existing approval or just decide a shortage is okay for profits or whatever, will cause relapses. Which leads to the downward spiral back into addiction.
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