In my experience, the leap to heroin from other drugs (because everyone knows heroin is a bad idea) is made easier because you get to a point where you understand that it's all essentially the same. The difference between being addicted to oxys, for instance, and being addicted to heroin is like the difference between being an alcoholic that drinks a case of beer a day and an alcoholic that wakes up and downs a pint of liquor. They're kinda the same thing, essentially, just one is cheaper, faster and easier and kinda better, but a lot stronger and more serious, which is fine. Stronger is good. Once you're at the case of beer a day stage and you think "I'm doing fine. I still got my job. I'm not fucking up my life." it makes sense to save money and go with the real deal because it becomes harder, more expensive and inconvenient to get the same buzz off a case of beer a day. Now you need like 2 cases and that's hard to drink and inconvenient, it costs way more, but you're still thinking "I'm fine" without realizing that there's now this visceral draw toward more and more. It's become engrained in your life and turning away seems unnecessary and kinda scary but keeping going toward the cliff gets easier and easier and more attractive. Then you get sick and actually need it. And your love affair grows because you get clean and think "eh that wasn't so bad. Lemmie pop back in for a little while and I'll quit again." and you get that awesome buzz you got in the beginning again after you've been clean for a while and the cycle continues. I don't think many heroin addicts don't quit because they can't as much as because they'd kinda rather not... plus they can't. Heroin withdrawals are no joke, but if you really wanted it - it's only temporary, right? But do you really want a life without awesome hay-ron? Not really. Yes, but no.

To cut this short: the scariest part is how unscary it is when you're in it, until you realize that it's got you by the balls. It's actually quite pleasant for a while and very manageable. It takes a while to completely go off the deep-end and I'm not sure people who do are even really aware they have, if that makes sense.