Why so many smokers relapse after having been quit for many months

This is an except from my book, "How to Win at Quitting Smoking": 

If you wanted to drop weight, you need to be willing to change your food intake and increase your physical activity. This takes a commitment, making a Plan and taking action. Slowly over time the pounds come off.

If after six months you went to a birthday party where your favorite chocolate fudge cake was being served and this one time you are unable to resist treating yourself to an extra-large corner piece with lots of frosting, you would not gain back the pounds you lost (you would if you continued this way of eating, but not from one slip).

Now imagine if you are at same birthday party but instead of being tempted by the cake, the temptation is a cigarette. Social events are when you enjoyed smoking the most, everyone is celebrating, alcohol is involved and it doesn't feel the same without smoking. A friend is smoking your brand and offers you one. You slip, smoke it and the receptors in your head get inundated with dopamine. Your brain seductively says, "Don't tease me with one, I want the whole pack".

The dopamine makes you feel better, big red warning flags don't pop up and you give yourself permission to smoke another one. Within a few cigarettes, your brain expects to have the same level of nicotine it had been used to prior to quitting, and you will relapse to your previous level of smoking. It would be like eating "just one" slice of chocolate fudge cake and overnight gaining back all the weight you had lost in the previous six months. It will feel as if you had never quit. Many will get discouraged feeling all their hard work is for naught and won't try to quit again for years. Don't let this be your experience.