Habits, by nature, are easier and more accessible, and humans are lazy creatures with greater willingness to do what requires the least amount of effort. By contrast, hobbies require effort-- and this effort becomes its own reward.

Face your deepest fears and do what it is that you are scared of. I think the scariest part of quitting is the fear of failure. Failure is only an option if you allow it to be. Take your future back and kick the cigs to the curb.