If you're addicted because your life was roughly fine, but you discovered that a drug make you feel amazing, keep taking it too much, and get to the point where withdrawal is so painful that it's impossible to resist taking another dose to feel good again, then that's exactly how you describe it.

But if you're using heroin or whatever drug as a mental health treatment, e.g. because if you hadn't started using you would instead have killed yourself, then sure you'll still have the nasty withdrawals when you stop, but it's a totally different equation. For many addicts, taking illegal drugs is the only way to feel OK about life. Some of these people never manage to get clean, but the ones with this reason for addiction who do (or who try to) get clean, it can be surprisingly easy to deal with the withdrawals, because they're aware of how shit life was before they first started using the drug, and the idea that the rest of your life will be as shit as before you started using drugs can be a far more scary thought than someone who's life was basically good except for their getting hooked on a drug.

To quote one of the all-time great TV shows, and surely the best about authentic portrayals of drug users, dealers, and cops - The Wire - Waylon, a former addict and narcotics anonymous sponsor, says “Getting clean’s the easy part. And then comes life.” I guess that's true for both types of addict I've talked about, but it's even more true for the addicts who turned to drugs because they hated their lives than for people who had lovely lives until they accidentally got addicted to a drug that they thought was fun to try.