Since all this discussion about alcohol, drugs, and addictions is taking place in the parenting topic, I'll share something with you.
I only had one brother, we grew up in a upper middle-class area in a metropolitan city in a country ruled by the Catholic Church many, many years ago. Although there were some double standards as to what was not permitted to me and permitted to him, most of it was basically due to age difference. I was 4 years older and the first born, so lots of things my parents didn't feel confident with me felt confident with him moslty because they learned to let go with me.
He tried drugs for the first time at around 14 years old. It was not because there were easily available to him/us, he was curious and found a way to get them. He used on and off for the next 20 years. The last 5 years of his life he started using more, in quantity and frequency. He never finish his education, he never hold a job for more than a year, his marriage didn't last more than a year, you get the idea...
We both received the same level of love, caring, and help during our childhood. Both our parents were very involved parents and did all they knew to guarantee our success, but something was wrong with him that made him look in a different direction. My parents were never enablers and knew how to put firm boundaries, they were always available and loving but was kicked out of their house for using, they kept the relationship and tried to help him to no avail. One day my mom recieved the fearful call that he overdosed, voluntarily...
His best friend didn't have the easy life we had, his father abandoned his mother when the youngest of his 4 siblings was 4 years old, he was 10. His mother wasn't the best example, he left school to work and support his family, did unimaginable things during his young years. Drugs, alcohol, sex... you name it, he probably did it. Today, he is a very sucessful person in his area of expertise, has a beautiful family and still looks out for his siblings. As a side note the youngest one died of sida when there were no real resources for them, he was 24.
All this to say, you have no idea what goes in the mind of others, why others chose to use, or not use, who has an addict personality and won't ever be able to recover. It may not be you, but it may one of your kids, a family member, someone you love...
As parents, we can always hope for the best. We can give our kids the most solid foundation, but unfortunately, there is no guarantee that it's going to stick.