i saw an excerpt from some psych book that was talking about cigarettes. one of the big things about smoking is that it's something you can do while doing something else. it's a void that nothing else can fill. it read something like this:
What else are you going to do while watching TV? What else are you going to do while browsing the internet? What else are you going to do during your work break? so on and so forth.
this combined with straight up nicotine addiction makes it difficult to quit.
in terms of starting, it's probably peer pressure that starts it most. some kids do it because their friends are doing it, some people think it makes it look cool. i think right now it's "cooler" to smoke weed, at least where i live. everyone i know who smokes weed or dabs also vapes or smokes cigarettes, so sometimes they go hand in hand.