Everything affects people differently. Tens of millions of people have smoked tobacco over the past couple of thousand years and never developed cancer.

My father smoked so many cigarettes, he damn near killed himself. He developed emphysema and only had 20% capacity of his lungs at age 48 and quit smoking at that point. He lived to be 74 but NEVER developed cancer.

On the other hand, there are cases of people developing lung cancer who have never smoked a cigarette in their entire lives.