For me, at the time it was the realization that I cannot continue to smoke and continue to play the trumpet. My lung volume and strength really suffered. But instead of stopping to smoke, for many months I played less and less trumpet.
What put me through the phase of actually smoking the last cigarette and becoming a non-smoker again, was one of the books of Allen Carr, I don't remember the exact title. Looking back, it was awfully written, and I had to will my way through believing the narrative, but it worked. That was 27 years ago, and I didn't have one cigarette since, no cravings and no replacement either.