Funny I was just watching something on YouTube the other day about soldiers who stayed addicted to substances and those who didn't. Having a good support systems helps a lot, plus having something fulfilling to do once home... careers, running businesses or whatever. But yes, a lot seems to come down to biology and then it gets nurtured by environment, at least from what I've read.

My parents did a great job at scaring the holy living hell out of us when it came to drugs. They still scare me. The only thing I've ever really done is pot but of course that's nothing these days. Alcohol wasn't too big of a deal either. I grew up in a family where drinking a little wine or a sip from a mixed drink on special occasions was perfectly ok. In my party days it always seemed like the kids in families who were really suppressive about it that ended up going berserk with it. I grew up in Mormon country though so that probably explains that!