Being hungry. Being Anxious or upset. Being bored. Being alone. are some of the common triggers. Human create rituals and associate ways to cope with certain situations these people has taught their body to deal with situations with smokes.
I'll explain on it from someone who has tried them before and has seen people around struggle with the addiction:
The problem with smoke is that it is not big and intimidating. Lighting a cigar and smoking it for first time may give you a weird mouth taste but it is still more bearable for many than drink beer for first time. It is accessible, people around you do it, and it seems like it is not a big deal. It is easy taht by curiosity to understand what is what they like about it, peer pressure to fit it, etc drive you try one puff...
You decide your first time, or at least you feel that way. You will not immediately will be hooked to it, which makes people sub estimate it, a few more times with your friend smoking one once in a while telling yourself you are not addict to them because they have been given to you , they are few in between and you don't feel anything 'weird' yet... few realize that they are not longer bother by the taste, they are getting used to it and slowly start relating that talk in the work break or meeting in the park with it. It is a gradual thing you don't notice, because you think you would act the same way without it but slowly you start smoking more often.
This is the step I never passed. I never bought a package on my own. but many will do, again just to pass the feeling of asking for one or brag about you bought one for first time. having the package means they are accessible for you at any time you like them, no more depending with friends.
No meeting with your friends and feeling bored. nothing to do. Taking a cigarrete and lighting it takes less than a minute. Once again it is gradual. you buy the second feeling in control because you say to yourself you liked the convenience, for a while many will keep believing they are just doing it because they feel like it. many discover their addiction when say they don't have enough to afford one of their own abruptly.
Nicotine kicks and gives physical symptoms as well as making your brain crave it heavily, which will turn into thoughts of finding a way to find yourself just of one cigarrete to calm it. It feels just like you have a strong habit that it is weird not to do so. Unless you by then area heavy smoker you may still deceive yourself into minimizing the kick into bad routine you created for you.
Now it is when the person may decide to to quit either gradually or cold turkey... or decide it isn't that bad and that the relation between throath cancer and smoking is mere statistics and no real connection has been proven and other justifications.
The big problem with cigarrettes is that almost EVERYBODY sub estimate them, specially people who has never smoked and despise the habit in others. They think people don't try because they see the people saying "I'll quit" and then find them at the petrol station buying another package. They think the guy is being half hearted.
Well, most of them are heavy smokers that as soon as they try to quit they will feel the withdrawal sympthoms hit them. In a matter of hours they have physical stuff headaches, body numb, throat excessively dry and more things that really are not that easy to bear as well as your brain going crazy, you 'need' a cigarrete. It is not a matter of I'd like or want one anymore. The physical part last around a week, so most of the people we wsee trying to quit in a day are back in a matter of 3 or 72 hours. They didn't start half hearted, they were firm but got strained and gave up. the more times they fail the more fear they have of the withdrawal symptoms and less confidence in themselves to overcome it. having people around just mocking you and minimizing your struggle only makes you as the smoker stop bothering with it. people still think it is funny and when you say you want to quit they say things like 'suuure. We'll talk in a few days".
I used to be like that with my mother. I mocked her habit a lot. "don't smoke. never start" she'd say holding a cigarrette. I would mimic taking off a puff and say with her voice "this is so baaaad" putting emphasis on the mixed signal she sent me. She say she really wanted to quit. Give me a heavy speech and in four days be back at it. next time I wouldn't take her so seriously. I chuckle when I see her next again with it. I knew it "she didn't mean it, deep in her she really doesn't want to quit". I was no aware of the difficult it actually means for people that are already into it. I am not laughing or minimizing or showing not interest for anyone who express the same need to me any more. I am not going to be cynical about it.
I still think there is a part of you holding you back and that is a determinant to effectively quit or not, but it is not the physical what is the hardest to deal with. After some days it is your brain what gives you the battle since basically "you want to quit, but you are desperate to smoke". from these two conflicting forces guilty, anxiety, frustration, a feeling of being trapped, feeling week, worrying about how would you in the future deal with the moments you calmed with the cancer sticks. you need a mindset and something very big that drives you through those hard times with your brain so you don't get so discouraged you resign.
Mix that with misinformation about risks and stuff. it seems like many link lung cancer but not other consequences more common and as frightening like getting strokes.Some people really don't see it as a big thing, they think the consequences will be far in the future. They feel it is an okay trade the yellow fingers, less breathing resistance, and other little details for the relaxing smoke.
It may seem like mind blowing but I think we all have in one shape or another something we enjoy doing and find a way to justify and minimize the consequences on our health. Over eating, not eating enough, drinking, eating junk food, not doing exercise three days a week, no brushing our teeth often, no visiting the doctor for preventive tests as often as indicated, etc... it is not that a normal of a conduct.
I think without a real huge drive it is very difficult to quit. So next time don't be preachy, all what you may want to say they have heard it many times already they have chewed it themselves and rubbing it in their faces will just make them defensive. Be supportive if they say the want to quit and put your cynical side that already believes he is doomed to fail aside. Help to come with options and ways to counter the brain common thoughts pro-smoking that will flood your friend soon enough when he cut of some of the habit. Enthuse to not give up. You don't give up on them if they want to quit and fail.
Not everybody wnats to quit. i found a friend doesn't want to quit except fro money reasons but as soon as he finds a way to secure his cigarretes he feel no need to try to quit or reduce his smoking, he doesn't care about the health risks with it. I have come to accept that and resign to that, those times he tries to reduce I help him with ideas and give him support by standing his irritable moods and not mocking him if he feel very week and sounds desperate for a tube.
Can't change the world. Each to its one. I am happy I am not smoking and I'll keep it that way. I am happy not being the jerk that gets scandalized for smoke in the area I am. I am happy I tried in the past and had the experience I learned from it even if many people won't approve of me thinking this way for the last line.