I quit back in '91. I was at 3 packs a day and basically disgusted myself out of the habit. I think I've told 3 versions of how I quit (all true) but really it was just self disgust. Now, I can't believe anyone smokes. It's horrible to be somewhere after someone has been smoking. It's horrible to talk to someone that smells like smoke. After a campfire (which we do frequently) I have to shower and change clothes.
I started smoking at 14 and quit at 21, and at 21 maxed the Marine Corps pft in NCO school with a 17:55 3-miles, so it wasn't health at all. I was just tired of it.
My uncle (deceased these 20+ years from a shop accident, God rest him) told me when I was 16 and working in his shop in Garland, Texas, that he woke up one morning without any smokes left, realized he was tired of running out for smokes like a slave at any hour and right then dropped the habit. Myself, I dropped the remainder of a pack in a garbage can at the airport in Des Moines and when I got off the plane at Pearl Harbor I was a non-smoker.