I know a guy who has smoked one cigarette a day, for about 70 years. One cigarette, at 4:00pm or so, for his entire life, pretty much. He usually has his one beer or vodka tonic at the same time, but, not always. One drink per day, one smoke.
He was running half marathons until his early 80s. Says his feet hurt too much for that now, but, he rides his bike a lot. Good shape for an old guy.
I've asked him why he didn't just quit, but, he doesn't have a good answer.

I never started.

Best,
Ted