I am in the same boat with the teaching. My #2 reason for quitting after "Live a long life" is to be a true role model to the students. They don't see me smoke, HOWEVER, I do live within the boundaries of my school, so there's always a chance. They're middle schoolers, too, and they are so prone to such risk-taking behaviors I feel absolutely implored.
If people can't find any other reasons and are involved with kids, BOOM, that's a prime reason.