I've read study results that support the idea that children of alcoholics are much more likely to become alcoholics, even if they are adopted into non-alcoholic homes. (I don't know the study name or researchers)
I think addiction begins with a genetic predisposition and environmental stressors (and exposure to the addictive substance/behavior). If someone has a high predisposition, then they might need less stress/trauma for the addiction to kick in. If someone has a low predisposition, they might need higher stress or exposure for the addiction to begin.
Both my parents drank way too much. One of my siblings and I both drank very little before realizing that there was a problem. That makes me think a genetic predisposition and past trauma/stress played a big part in me developing an addiction. I did not have to work at it.