Regarding Carbs & Nicotine.... take it from an ex smoker. I was a heavy smoker for about 12 years, but quit over 25 years ago. Nicotine is one nasty habit. Very hard to give up. Even for 1 day. And one drag off a cig after 1 week or 1 year, will most likely put you right back where you were... a slave to nicotine.
OTOH, carbs can be given up relatively easy.... but starts to get difficult fairly quickly.

But here's the biggest difference.... Carbs are required to live... Nicotine is not.

I pride myself on having given up some pretty bad addictions in my life..., but I cannot, for the life of me (literally?), permanently control the carbs and cut the sugar. The only reason my numbers have been good the past several years is meds. And THAT really sux.