The tenacity of smoking: A pal of mine is a practicing psychologist who put himself all the way through grad school by managing a bar. He smoked constantly. When he got his Ph.D., and incidentally proposed marriage to Ms. non-smoking Ph.D, he realized he had to quit. That was 16 years ago. He tells me that about once a year, he still craves a smoke. And that from a man who knows the human mind very well indeed, including presumably his own.
My pal also told me that he read a real study, not the barroom kind of study, about ex-cons in a half-way house. These ex-cons had been addicted to everything imaginable. The study concluded from the ex-cons that barbiturate withdrawal will indeed kill you, if not done under medical supervision; that heroin withdrawal will make you WANT to die; that alcohol withdrawal will make you THINK you're dying; but that tobacco withdrawal is the hardest withdrawal of all. That's breathtaking (no pun intended in advance.)
Third and last chime-in: when I quit smoking, I read the usual phases of recovery (three days=end of physical addiction; one month=lungs start recovering; etc.) One thing that stuck in my mind, because it seemed so far-fetched, was that the very last sign of recovery didn't take place until four-five years after quitting. That's regaining one's full sense of smell and taste. I'm here to tell you that five years after quitting cigs, rather suddenly, I'm smelling and tasting things in a whole new way. Those studies can be true sometimes.