Being aware of a bad thing

Why do people smoke even if they know that it is harmful?All of smokers are aware of its harms.Also,it smells disgusting,it is expensive,it causes so many physical problems and it kills quickly.There are two main causes which lead to smoke ; emotional problems and choosing bad friends.
If people have emotional problems,of course,they want to get rid of it.They think that smoking is a solution.The first thing they think smoking helps them when they try to cope with stress,they feel as if they were relax while smoking (nicotin may cause it ) but it is mostly occured by psychological.They also like smoking.It is believed that,especially among Turkish people,they don't think they will be ill.They always say "nothing will happen to me",and these are my favorites ;"if it is very harmful,why is it sold ?" " i can give up,but it won't be able to give me up.It is my faithful friend" "cigarette is better than a bad friend"
The other reason is,as i said ; choosing bad friends.Of course,you can be good friend even if you're smoker but you must prevent your non-smoker friend.In contrast,most people don't care about it.A non-smoker friend looks his friend and says "if he smokes,i can also smoke.He is not superior than me " then he starts to smoke.Neverthless,the other friend who is smoker supports him and they begin smoking together.It generally happens at the age of 10-20.Youngers want to prove themselves and they think that smoking is the best way.
We can not do anything to prevent smoking.Even if we know it is harmful,we smoke.Neverthless,if we want to understand that it is really useless,we can give it up easily.Everything depends on in our heads