Its been two and a half months since I've smoked, and I can tell you this much...once you are hooked, its extremely tough to stop. The chemical nicotine actually changes your brains physiology in such a way that you become dependent on the chemical reaction created by the nicotine.
Aside from that, I don't really see it as stupid. Its a choice, a way of coping with the world and a choosing of an experience. That choice can and does cause health problems, but if you are willing to accept that choice, then I wouldn't call it stupid.