One day as I lit a cigarette someone said to me, "I used to smoke, and then I realized that I was the smartest person I knew who still smoked, so I quit." Later I thought about this and realized that I was the smartest person I knew who still smoked, so I quit too. Actually thinking about the smokers you know can be an eye-opening comparison.
When your job is almost entirely about providing immediate gratification for other people, smoking is something you do entirely for yourself and your friends. Even if it involves huddling in the cold.