It depends entirely on the level in which you smoke.

20 per day everyday is, inevitably going to be bad for you in the long run, however, just because you go out one night and drink alcohol doesn't make you an alcoholic, so if you only had a pack of ten for an entire week, it wouldn't really make you a smoker, to the extent that it wouldn't have half the effect that 20 per day would have.

So that's what i put it down to.