The first 2 years, I didn't realize I was addicted to them. I just smoked when I wanted, which was between every lecture and with my friends in the evening. Then I tried to stop.
Quitting smoking is weird because sometimes you can just stop, and don't feel the need to smoke (until a couple months later you get drunk and buy a pack).
Other times, it's really hard. As in horrible. Your brain is trying to trick you into doing it. Telling you that your girlfriend (who asked you to stop) will leave you if you don't have one and calm down. Telling you that you haven't seen (smoking friend) in a long time. Just like you can't perceive your blindspot, you can't spot your own irrationality. This, I think, is the biggest reason smokers don't quit. It's relatively easy to fend off cravings, but recognizing irrational, addiction driven thought is hard.
Anyway, so one day I'm in a medical stats class. The lecturer is making a joke about a graph. It seems to show smoking is protective against prostate cancer. Smokers are super unlikely to die of prostate cancer. It looks convincing. Smokers don't survive to die of prostate cancer. It convinces me not to smoke again. I make my way downstairs, and grab a bagel. I have an exam next period, and I'm behind in that class. I can't focus without a cigarette. I light up, and keep lighting up, and now it's 5 years later, and I'm not going to die of prostate cancer.
There is this idea that humans are rational entities capable of making free choices, but we know they are really, really not. Thinking Fast, Thinking Slow, a great (nobel prize winning) economics book explains that there are situations where humans predictably make bad choices. Addictions are one of these. If I were not hooked on cigarettes, as a smart, otherwise disciplined person, I'd be more sympathetic with this libertarians on drugs.