Cancer isn't something you can control, addiction is. He's been with DDP for months and looks great, if he wanted to drink he should have said "I'm doing really well, I don't want to go back to my old ways, I'm gonna say no"
LOL, I don't think you quite understand it. At all.
People don't WANT to continue doing bad things, but, when you get addicted to something, especially when it's for a long time, it's very difficult to stop doing it. Let's take smoking, for example. No doubt you know people who smoke. We all know at least one person who does it. A lot of times, they started for reasons like being in a group at school, someone offers, you start smoking. People don't grab a cancer stick because they WANT to get cancer. They make a decision that isn't a very good one, for whatever reason (peer pressure, etc.) Bad decisions are a part of life, we all make them. People just have different reasons for saying yes to things they should be saying no to. They think 'meh, just once, it wont do anything'. Then, it turns in to 'man, I liked the way I felt the other day, I am gonna try it again'. Then again, and again, and again....and you are now snowballing out of control. Your body craves it, you like the feeling, you feel urges to do it, or else you feel like you'll go crazy.
You don't just step out of it, it takes time. You have to be motivated to recover, you have to forget the 'happy' feelings you get with it, you have to learn to not depend on it.