Its largely true that nicotine leaves the body completely after 72 hours (3 days), and it is laregly the case that once your over those three days, quitting is a peice of piss.
The mistake people make I think is associating the very minor withdrawal symptoms of nicotine, with the incredibly major, physically painful withdrawal one experiences from something like heroin.
Nicotine withdrawal is a mild feeling of physical and mental discomfort that can be largely dissipated by eating some food, having sex, or going for a walk, or doing something else pleasurable.
The difference is that most smokers choose never to go through those symptoms cause they can easily go to the shop on the corner to buy some fags to make 'em go away.
DO you think those smokers would go through the same privations as heroin users to get their fix? **** no. I wouldnt have broken into a shop or commited a major crime to get fags when I was addicted to them. After 15 minuts the craving goes away anyway.
If your trying to quit you will experience roughly 2 or 3 major cravings a day for the first 3 days. These last about 15 minutes each and then simply slink away. Find something to do for those 15 minutes: Anything at all, punch something, jerk off, whatever it takes.
But dont beleive you are gonna spend those 3 days in a sweat-soaked junkie delerium, cause you are'nt. Your body will largely be sending you big waves of thanks for releiving it off the years of stress you've been putting it under by smoking.