I have quit cigarettes successfully (for ~10 years now) and found it wasn't too difficult. However, I have known people who could quit indefinitely and pick it back up without issue and people who are going through rounds of quitting, returning, quitting and so forth.
I personally believe there are additional elements involved that could be genetic or psychological.
I used to both smoke and extensively used pure Nicotine (gums, sprays etc.)
In my opinion, majority of the people who are stopping Nicotine (not just smoking) approach it as an incredibly hard challenge. The process is demonised and described as something that is really hard to complete. That's exactly what I would like people to think if I'd be to work in a marketing department for tobacco corporations.
While there is a longer story behind it, I quit cold turkey in March this year. This time was much easier - I didn't approach it as something that is hard to do. While this might sound banal, I focused on what am I getting out of it, not what I'm loosing. Everything, from my gums to my muscles got better.
Nicotine in its pure form is definitely great brain stimulant, I'm still a big fan. I just don't think it's worth the cost, both from financial and health perspective to use it often.
cigarette smoke also has a bunch of other stuff, including MAOIs. it's definitely not _just_ the nicotine. iirc, cigarettes also have additives to make the nicotine hit harder / cross the blood brain barrier faster, which probably doesn't help
I personally believe there are additional elements involved that could be genetic or psychological.