At least for an ex-smoker it also takes a lot more discipline. It's the habits that are the hardest to break. After a good meal or during a work-break the urge to light up is the strongest, even when you quit long ago.

Moreover a cigarette provides a nice time-frame and the illusion of of doing something. You can have a "one cig break" or a "two cig break". And you have something to do while thinking, which helps with the process (at least it does for me).