I've been smoking for about 4 years now. I have stopped smoking twice (I can't think of it as "quitting", because that word implies agency), each time for around two months, almost spontaneously, without even thinking about it, planning anything, or having to try at all.
Looking back, I realized that what the two episodes had in common was that both those times, good things that I cared about very much and could potentially change my life forever were likely to happen (though they didn't!). So the best explanation I have is that "hope" is what made me stop smoking; had those things happened, I would have liked to experience them for as long as possible.
So instead of following one-size-fits-all instructions (which have not helped me the 8 times I have tried to quit), I've decided I'm going to try and put myself in situations where good things with long lasting positive effects might happen to me, as often as I can, since that seems to actually help me.