Nicotine is more or less like caffeine. If you can't drink your usual cup of coffee or tea, you may get a headache and be a little grumpy. After a while these "withdrawal symptoms" will disappear. What makes cigarette withdrawal so difficult is definitely contained in the thousands of additives found in cigarettes today. One of them might be monoamine oxidase inhibitors, I do not know if they are naturally present in tobacco, but if someone responds to them and want to stop smoking, it could make it very difficult.