Two things to say about this:
1. I have, apparently, reached the age at which people who are younger than me will die tragically and unexpectedly, but having had enough time to get themselves into trouble and start trying to crawl out of it. It's not Philip Seymour Hoffman throwing away a long and distinguished acting career, and it's not quite DFW succumbing to the pressure of early success. It's someone whose career seemed to be generally on the upswing, and was well-liked by a lot of people. If that's not enough to frighten you, I don't know what is.
2. Related to that last point, I have never in my life done any kind of drug and I've never had the least desire to. When I was younger, it was out of sheer love for my brain and an aversion to doing anything that might mess with it. Now it's with a few decades of seeing that the best case scenario for use is trying it out for a short period where you're young, are not one of the demographics targeted for prosecution on drug-related charges, have no mental health issues, and have the benefit of a stable (or at least good) home life to keep whatever you do moderate and limited. I know people who had the benefit of all of these and still lost years or decades of their lives--and those are the ones who have survived.
For both of these, I credit an adolescent viewing of Trainspotting. Like Renton says in the film, they're not idiots. They just have very little control over their lives. It's not (entirely) their fault, because addiction has complicated social, mental, and physiological components that cannot be willed away. But the easiest way to avoid having to solve that later problem is never to start.