Seeing one side of a sheep only reveals half a sheep. There might be nothing on the other side.
Smoking long enough ensures that you will quit forever, you just won’t be alive to know it.
The same is true of quitting, of course. Aside from rare situations such as a beheading it is hard to lose consciousness while being reasonably sure that you won't regain it, if only briefly, and even the guillotined could wake up post-singularity and start smoking again!