Just a thought, please read through fully before classifying me as a shameless opportunistic trader worm.
Ok, now that you are on my side, I think smokers have a hard time quitting because of
(a) the thing itself and
(b) the way non-smokers treat it as a binary thing - he used to smoke, then he quit, but then he started again!
Life switch was off, then came on, then went off again!!
That is not how it is. Smoking is a progression - increasing or decreasing or plateaued.
If you go from 2 cigs a day to 3,4,5... pack, 2 packs, it is increasing. From 2 packs a day to 1 to 4 cigs, 3, 2 it is decreasing, if you stay at 1 cig (or 5 or 10 or whatever) a day, you are on a plateau.
The basic terms now cleared, let us see when you tend to smoke more and when less - stress is an obvious factor.