Two reasons quitting smoking is hard

First, this research finding from Yale:

When cigarette smokers first stop smoking the number of nicotine receptors in the brain is significantly higher when compared to non-smokers, which may explain why it is so tough to quit...

Second, the tobacco companies are making it harder for you to quit:

All tobacco brands have been increasing the nicotine dosage in each cigarette steadily during the last six years, says a report from the Massachusetts Department of Public Health. The overall increase has been about 10% during 1998-2004.

Marlboro, the most popular brand, has been steadily raising the dosage in each cigarette. Kool, a popular menthol brand, has had its nicotine dose increased by 20% in six years.