If a stressful day is enough to give you a craving difficult to resist, I think that saying "anything less than complete abstinence has a chance of kickstarting the habit" is a misleading statement of how it works. It might be more accurate to say that every cigarette you have is one cigarette closer to having a habit you need to kick. It seems, in fact, that there's sort of a gradient of average craving from abstinence all the way up to two packs a day, with variances around those averages. It seems a bit obfuscatory to suggest that "complete abstinence" is the deciding factor, especially when considering the question "When does complete abstinence start? Why doesn't it start after the next cigarette?" After all, the "real" complete abstinence has already failed, if you had to quit smoking in the first place.

. . . but that's kind of off the topic of the worksheet example.