I smoked for 24 years, then quit. I was off of nicotine for over three years, when a combination of events caused me to take it back up in April. In less than a week from now, I'll quit again.
I've toyed around with other addictive substances that shall remain nameless here, and had no trouble at all after the decision to leave them be. Tobacco is tougher than all of them combined.
I could be fooling myself, but I don't expect to have too much trouble kicking the habit this time. Practice makes perfect, eh?