I've never understood this advice...
no one knows whether or not they are going to become a full blown addict. Granted, you are correct, some people can enjoy certain drugs once or twice and have fun while others chase that dragon from the first experience..
I just tell people to not even bother. Save them for when you need them and are prescribed for pain. If I could go back I would've never bothered at all.
For many, including myself, it starts as a once in a while thing...and as I stated, some can push the stop button any time they please, but for others...it just develops into a horror story that most couldn't even dream up in their sleep without even realizing it until it's too late.
Opiates will turn you into a person you couldn't see yourself being even in your darkest days.