Smoking is a bad habit and it also has a nasty habit of coming back to you again and again...
My parents were chain smokers in their early twenties. They were trying to quit smoking on and off before we, the children, came.
The first reason that Mom used to motivate them to stop smoking was the amount of monthly cigarette money. It was so huge! Imagine burning 3 packs a day -- times 2!
The second reason was us. As young kids, we always had colds and coughs because our lungs were irritated by the smoke from their cigarettes. Even though they often tried to smoke outside the house, their addiction to smoking would inevitably attack during the times they were taking care of our baby needs.
Mom forced herself to quit using cold turkey. She found herself some hobbies that helped banish boredom when we kids were sleeping. Ironing clothes, painting, and writing.
Dad was able to stop completely when my youngest sister was five years old and was able to tail after him whenever he went outside to smoke secretly. She would shriek like a siren the moment she saw Dad with a cigarette. It was effective.
After more than ten years of non-smoking, they both admit to still feeling a secret craving for a cigarette. Thankfully, the high price tagged to a stick or a pack of cigarette is enough deterrent.
Another important obstacle is the hobby that lasts until now. Mom has become a full-pledged writer. And since Dad always supports her, he was also able to stay away from smoking.
I could just say 'love and family' to answer this question but I always feel that our story is good enough to tell.
Thank you for posting this question. :)