Maybe it would help to sit down, close your eyes, and think about why you quit. Bring back all the reasons you mustered the strength to go through 72 hours of physical withdrawal from nicotine. Try to bring back the feelings. How it felt to be a drug addict, constantly feeding the addiction to nicotine.

Remember that it's not about that 'one' cigarette, it's about the whole addiction - everything. When it comes down to it, do you really want all that back in your life?