When I wanted to stop smoking, the idea of never smoking again would make me stressed and make me want to smoke.
The solution was I put "have a cigarette" on my to-do list, at the bottom.
So I never quit smoking, I'm definitely going to have a cigarette at some point, when I get round to it - just after I've re-tiled the bathroom, wrote a novel, made a computer game, taught the cat to play piano, finished a series of 100 paintings, wrote an album of songs etc...
... so it's over ten years since I last had a cigarette, and there's only a thousand or so things to do on my to-do list.