We all fall sometimes
Always remember that that demon is lurking in all of us... we must be vigilant. Regardless of how we look at it, We are addicts, and even the best of us can slip up and fail every once in a while.
I think it's an individual matter. I've not slipped once in 3 years. Once I had a vape that lasted me all day that was it. I've not had one smoke since, and never will again. The very idea disgusts me. When I first started vaping the early equipment I got didn't cut it, and rather than ever smoke another cigarette I just went after better and better equipment, until I was satisfied. I cannot imagine the circumstances under which I'd ever smoke again.