I quit smoking 3 times in my life. The first time was with hyponosis, it lasted 16 years. I started again during my divorce. I smoked for 6 years and quit with Chantix. After 6 months, I smoked again for a few weeks and quit cold turkey.
The entire time I smoked, I knew it was bad for me, but smoked anyway. I still miss it, but don't want all the side effects of smoking, like heart or lung disease or even smelling bad.
Some people self-medicate with tobacco and find they are depressed and anxious without it. The addiction to nictoine is physical and psychological. You only quit when you want to quit and even then, you might need help.