Every single time I've stopped after picking up the habit (3x now) it's for a couple of reasons:
It makes my dating pool more shallow. I don't mind a smoker, but other people do, so why limit myself?
It fucks up my car/clothes. Burn holes aren't cute and tobacco stench isn't easy to remove.
It physically hurts after a certain point. When I can feel my body hurting I try to listen to it, and there is no benefit to smoking.
How? I stopped buying them. Cold turkey, cravings and irritability and all. If I didn't buy them, I couldn't smoke them. It takes a lot of willpower but it is possible.
Every time I pick up the habit again it's because I am in a shitty place in life and want to punish myself for being alive and "kill myself faster". Pretty bleak, but it's true. So now that I know what triggers me into smoking, I am more mindful about my moods and how to dig myself out of the hole of self-loathing before I do destructive things. It gets easier with practice, that is for sure!