My grandfather was an avid smoker. He was playing basketball with me at the park when I was only a kid, probably six or seven years old. As he was smoking a cigarette, he looked at it, and I suppose it dawned on him that it tasted awful. He proceeded to flick it and never smoked since.
My father is also a smoker and still smokes to this day. He did all kinds of drugs in his day but the hardest one to let go of he says, are his precious cigarettes.