Your wish to smoke is not caused by the decrease of nicotine levels in your blood, which what many people want you to believe. It's because your mind is trained to desire cigarettes at various points during the day.
There's a very simple example to demonstrate this. Do you smoke every, say, hour? No, you smoke when you're on the phone, when you're in the car, or right after you've had a fight with your wife. Your smoke to relieve stress, not to satisfy your craving for nicotine.
You do not hear yourself say "wow, I could sure go for some nicotine right now." Instead, you say "huh, let's take a break and have a smoke." There's a key difference there, and it's something that few people who want to quit realize.
Just as smoking is something your mind desires, quitting has to be done by dealing with your desires directly. You have to figure out what your mental triggers are and how they work in order to stop your urges for cigarettes. The nicotine patch, gum, and the like do not work because they treat your physical addiction to nicotine.
You've probably heard of a ton of people who are on the patch yet still want a cigarette. If cigarette addictions were physical addictions, that would never happen because their want for nicotine would be resolved by their replacement therapy, but it's not.
Again, smoking addiction is caused by your mind and its want for cigarettes, not from any sort of physical conditions.