I worked on quitting for some 20 years. I started when I was 14, peer pressure of course, had to look 'cool' for my buddies (who all already smoked). I finally quit at the ripe age of 57, some four years ago. I did not get any physical/chemical withdrawal symptoms from any of the methods, and I tried all of them, multiple times each just to be sure. It did not take many to come to the conclusion that smoking was more of a behavioral issue than chemical dependence, at least for me. Yet it was equally clear that it has a chemical origin. And I was not blind to the medical reasons for quitting. It was just that neither reason nor will would have any practical effect. Each quitting method led to some small interval - weeks to maybe a couple of months - of not smoking but yearning after the odor trail of those who did, followed by renewing the habit.
So I started to see what I could learn about the mechanism of the addiction. Something about the training one undergoes when starting induces a very low level behavioral pattern, something that produces a neurological reinforcement associating the ritual of smoking with its physiological after-effects combined with the immediate social approval. Something that thereafter remains immune to frontal-lobe reasoning. From other life experiences I already had a pretty good working hypothesis that laying down or changing any enduring habit takes between 6 months to a year to become autonomous. An independent hypothesis, but one that I finally recognized as germane to the smoking problem, was that negatives in verbal instructions to ones' subconscious (or others) are lost in translation. "do not think of Pink Elephants" is the exemplar phrase. The not is dropped and the associated concept activated.
And I had to find something that recognized that basis with which to attack smoking.
Reading Dr. Jeffrey M. Schwartz's books on his OCD research gave me an underlying theory, and the regularity and acceptance of weekly Nicotine Anonymous meetings gave me the framework on which to build the habit change (forget the 12 step nonsense, all I needed was an ongoing community with a smoking focus. There are no alternatives). Rather than working on "not smoking', the idea became to just pay attention without critique to my inner thoughts when 'smoking' became activated, and simply let them pass. No negatives involved. One year later I smoked my last cigarette.
I am still a smoker. I just forgot to smoke today.