Some smokers can quit, others will never be able to do so. My dad is in the former category, my mom is in the latter. I'm somewhere in between.
I smoked for about a decade. Really smoked. Unfiltered Camels, minimum of a pack a day. Sometimes two. I have a high-pressure job and could suck down a coffin nail in the time it takes most people to take a shit--one minute to the door, two minutes between light and all gone, one minute to get back to the desk.
The only way I could quit was to get away from it all. I took two weeks off, filled a backpack with enough food to last and wandered solo through the wilderness where there were no cigarettes, no pressure and plenty of hills to make me realize that I really needed to quit. At the beginning, I was wheezing up every hill. By the end, I was doing pretty good.
I relapsed after five years clean and smoked like a fiend for another five years. All it took was one weak moment, one "Let me light that for you" and bam: Right back where I started. Re-did the two-weeks-in-the-wilderness thing and I've been clean for another five years. This time, no cravings, which I can't explain.
Everyone is different, and while gum and patches and hypnosis and prescription drugs might help, I think it boils down to your body chemistry and desire. Mind over matter, if you will. Some people can do it, and some people can't--tobacco is that strong a drug.