In the reply you replied to, you can see that I am writing about how they may know the dangers but may not know to what extent the danger is (probably because they always wake up the next day). For instance, if a doctor told a smoker that his lungs are so damaged that one more cigarette, he’d be dead, I can guarantee you that the addiction will vanish because now he knows that it’s to the extent his life would be gone in the next try.
As already said, most of them know about damage made by cigarettes. I really doubt that words like that one more cigarette could be last one would stop him. Now in my country on package of cigarettes there is images of damaged lungs or something similar, not sure how much it helps.
Probably they don't stop as long as they feel ok and don't get lung cancer. Though, my grandpa even with lung cancer didn't stoped smoking almost until his final days...