There are many reasons why someone would begin smoking. If they start when they are young, it is usually due to peer pressure which is at its most intense during adolescence. It appears to be cool and its easier to fit in if you do what your friends do. Once the addictive elements in the cigarettes have entered the body, they begin to create an addiction immediately.
Regardless of all medical evidence to contrary, an addicted smoker will continue to smoke, even though they know it will harm them. Despite a huge cost to the smoker of keeping the addiction, they continue to smoke, the addictive chemicals in the cigarettes are binding to them to the habit.
Young girls often believe that smoking will help them lose weight. It is true that smoking serves as an appetite suppressant but the resulting medical problems are clearly not worth it.
Smoking is a social plague, it is dangerously addictive, medically carcinogenic, expensive, smelly and unpleasant. Only a junkie would put up with all that surely?