There are several reasons why some people have a harder time giving up cigarettes…
Dependence. How long you have smoked matters less than how much you smoke. Typically, people who have more than about 15 or 20 cigarettes daily experience worse withdrawal symptoms than people who smoke fewer cigarettes. Even so, two people who have smoked the same number of cigarettes for the same length of time still can have different degrees of dependence. Heredity may affect dependence and severity of withdrawal.
Motivation. People who have had a heart attack—or other health scare related to smoking—often find it easier to quit.
Preparation/practice. To improve their chances of success, smokers should set a quit date. Before that date, they should start going without cigarettes for part of the day—for example, while driving or watching TV.
Helpful: Most people make five to seven serious attempts before they can remain cigarette-free. With each attempt, they learn which situations make them reach for a cigarette—and what they can do to fight the urge.