I smoked for 3 to 4 years, about a pack and a half to two packs a day. (marlboro menthol lights)
I quit smoking when I got a call that my Grandma was in the hospital fighting cancer and that her diagnosis didn't look favorable. Right after I got the call, I walked out on my patio and started smoking a cigarette (stress smoke) and started thinking about all the good times we had together throughout my life. Her and my Grandpa raised me and my two sisters for quite a few years while my parents were going through a divorce, so not only would I lose my Grandma, but in a way, my mom too.
While I was smoking, I kept asking myself why this was happening to her. She was a staunch church goer her entire life. Never drank alcohol or smoked tobacco. I do know that she worked as a waitress in a restaurant for many many years back when it was acceptable to smoke in them. I won't attribute all of her cancer to second hand smoke, but I will say that it probably didn't help matters.
My wife and I (We had been married for a couple weeks is all) took off the next morning and drove 4 hours to see her. When we arrived, my entire family was there. My Grandpa, Aunt, Uncles, Parents, Brother, Sisters, & Cousins. When we walked in the room, there was total silence. My Grandma couldn't talk, she couldn't eat, she couldn't move. We stayed for a couple hours, it was silent with lots of tears virtually the whole time. Because we had to get back to Salt Lake, we said our good byes to my Grandma and the rest of the family and started our journey back. As we were making our way out of the hospital, it started to hit me, that could be me in 30 years. My wife was a few months pregnant with our first child and after seeing how difficult it was for everyone to deal with the cancer and my Grandma's health, I decided to eliminate the one obvious cancer causing problem that I had. I didn't want my family sitting around my hospital bed watching me die from cancer so anything I could do to prevent it, I did (yes, all of that went through my head as we were walking out of the hospital...with lots of emotions).
When we got out in front of the hospital, I reached in my pocket, took out the pack of smokes I had, and threw them in the garbage by the door. I got a call the next day from my Dad as I was getting off of work to tell me that my Grandma had passed away.
For me, quitting smoking wasn't difficult because I truly never wanted to smoke another one (mind over matter).