Smoking is a hard habit to break because tobacco contains nicotine, which is highly addictive. like heroin or other addictive drugs, the body and mind quickly become so used to the nicotine in cigarettes that a person needs to have it just to feel normal.

People start smoking for a variety of different reasons. Some think it looks cool. Others start because their family members or friends smoke. Statistics show that about 9 out of 10 tobacco users start before they're 18 years old. Most adults who started smoking in their teens never expected to become addicted. That's why people say it's just so much easier to not start smoking at all.

source:kidshealth.org