Hum, it’s all about the neurotransmitters, really.
Our “base triggers” are still the same they were when we communicated in “ugh ugh”, namely:
a) Fight or flight
b) Sex, or the chance thereto
c) Very very nutritious meals
These are the three base components that fire off all those happymakers in your brain that will, as a reward, swarm you with either Adrenalin and Norepinephrin (fight or flight) or your body’s own opiates (food), sex is a mix of both.
Your body, smart as it is, is trying to keep all of that in a nice equilibrium in order to keep you going.
Add stimulants, and your in trouble. Why?
Your logical mind “feels good” for not smoking, because “logically/consciously” you know you’re doing the right thing, your body however, would really much rather have that extra burst of “happy transmitters”, thus, you’re not addicted to the “logical” feeling good, but that flood of happy little substances.
Your body/brain doesn’t feel a need to “reward” you, because you’re not supposed to inhale toxic fumes/smoke to begin with, and on top of it, now that you showed it a way to get all that good stuff from the outside it is even grumpier for you not continuing.
All strongly simplified of course