A while back (some years perhaps) on Reddit there was a story about someone who basically documented their experiment with heroin. It could have been a hoax of course, but most agreed it wasn't.
It was this person who was already doing milder illegal drugs. He goes to his dealer and dealer proposes something different this time. He decided to try heroin. Had pretty high confidence he wouldn't get addicted. Anyway he describes his first try. Then as weeks went on he periodically posted updated. He kept justifying going back to trying it. Gets addicted. Long story loses his job, girlfriend, goes into rehab for a long time. Pretty harrowing story.
I think the main problem is that lots of people who have heard the "try it once and get hooked" story realize that they did try it once without problems, and therefore assume that addiction won't be a problem. From once to a few times to regular use to addiction is a slippery slope that most avoids, but for some it can take several years. But none of them started it with the assumption that they themselves would get addicted, and along the way made up many rationalizations for their drug use. So in that way, this anecdote is interesting.
Sorry I tried to find it but couldn't at the moment. It was some years back and reddit's search is not the best it seems.
Anyway the idea was that many go in thinking they can handle but it turns out they can get addicted the first time and it can ruin their life pretty quickly.
It was this person who was already doing milder illegal drugs. He goes to his dealer and dealer proposes something different this time. He decided to try heroin. Had pretty high confidence he wouldn't get addicted. Anyway he describes his first try. Then as weeks went on he periodically posted updated. He kept justifying going back to trying it. Gets addicted. Long story loses his job, girlfriend, goes into rehab for a long time. Pretty harrowing story.
EDIT:
Thanks to japhyr56 who found the link:
http://www.reddit.com/user/SpontaneousH/submitted/