Spur of the moment attempts to stop smoking are more likely to succeed than planned ones, a study says.
More than 1,900 smokers and ex-smokers were quizzed
University College London researchers interviewed more than 1,900 smokers and ex-smokers about their attempts to quit, the British Medical Journal said.
Researchers found two thirds of smokers who stopped suddenly succeeded for at least six months, compared to under half of those who planned it in detail.
The study said planners possibly felt less strongly about giving up.
The theory is based on the idea that prior to giving up smokers have varying degrees of "motivational tension" which result in the decision to quit.
Motivation is likely to be high in those who take immediate action, but less so in those who opt to quit some time in the future.
In the study, 65% of the unplanned quit attempts had succeeded for at least six months. This compared with 45% of those who planned to give up in advance.
It has traditionally been thought that the best way to beat the habit is for smokers to go through several stages - thinking about stopping, planning an attempt and making that attempt.
The researchers said their findings do not imply that planning to quit is counter-productive.
Lead researcher Robert West said: "The results do not mean that we should tell everyone to stop without planning ahead, but they do tell us something about the state of mind of the smoker who wants to quit.
"Dissatisfaction with being a smoker creates a kind of tension. Then, when that tension is high, even quite a small trigger makes the smoker decide that the time has come to stop.
"If that decision is to quit some time in the future, rather than right away, then in some smokers it could indicate a weaker commitment."
Jean King, director of tobacco control for Cancer Research UK, said: "This is an interesting survey showing that there are different strokes for different folks.
"The new findings suggest that some people can stop on the spur of the moment and that is very good news for them.
"Others benefit from planning a quit date.
"In both cases people can always get additional support from NHS Stop Smoking clinics which have helped thousands of people give up by providing nicotine replacement therapy, support counselling and a timetabled plan for smokers if that is what they need."