I was a pack and a half a day smoker years ago. Tried to quit more than once but it wasn't until I started running in earnest that made any progress. I would go for a three mile run hack up a lung for ten minutes and stop to buy a pack on my way home. Now that's addiction. This was thirty years ago and there was no pills, gum or e cigs to fall back on. Cold Turkey was the order of the day. My GF's sister told me that she was hypnotized and it worked for her so I gave it a try. I don't know if was psychosomatic but I haven't smoked since. About a year later I ran my first of eight marathons and countless shorter races. I think replacing the smoking with running went a long way to staying smoke free. I was taking something out of my life, smoking, so replacing it with running went a long way to fill the empty space that quitting left.
Now when I see someone smoking it kind of repulses me. IMO there is no upside. It smells bad it's way too expensive and it's just about the worst thing you could do for your health let alone fitness.One other thing even after you quit it does not mean that you're not at risk of contracting lung cancer. My mother smoked for years but quit a few years after me. In her case it was too late. About five years after quitting she developed long cancer. So there is good reason to quit NOW. The longer you smoke the more damage you are doing.