These folks are sort of like pilots of a plane that has been damaged or depleted of fuel. Nobly they try to keep the craft aloft. And they keep fighting gravity to the bitter end, until they plummet to the ground, nose first.
If you were a passenger in that plane, would you want a pilot like this, one who refuses to give up on the original destination even if all indicators signal that your plane won't make it? As heroic as these efforts may seem, there is a better way. Wouldn't you rather have a pilot who took action in response to earlier signs of trouble and did whatever necessary to get you on the ground safely?
For a recovering addict, the pull of gravity is an increase in the potency of the draw of addiction. There are reasons the pull has become more potent. We need to address those reasons rather than just gritting our teeth and fighting harder.
One key weakener of willpower is fatigue. Harvard researcher Seung-Schik Yoo has demonstrated that sleep deprivation inhibits the capacity of the brain's prefrontal cortex (self-control central) to reign in the emotional reactions and impulses generated by the more primitive limbic region of the brain. Using functional magnetic resonance imaging (or fMRI), they demonstrated that when we are sleep deprived, we suffer an "prefrontal/amygdala disconnect" contributing invariably to "non-optimal decisionmaking in sleep-curtailed ... personnel ... as well as circumstances of emotional irrationality in an increasingly sleep-deprived society."
So here's a homework assignment to try out the next time you find yourself struggling against the pull of your self-destructive habit. Don't just try to avoid crashing, find a soft place to crash land. Don't just resist, prioritize rest. Don't push through your fatigue, push back from your desk. Instead of keeping your nose to the grindstone, smell the roses.
Think you can't afford to take a break? Well, one may be coming either way. You can't necessarily choose whether you'll seek a release, just which release you prefer. Proactively prioritize healthy ways of "crashing" and take them early on by relaxing, meditating, napping, and getting to bed on time or perhaps even early for a change. You'll improve the chance that you'll find your craft intact and fit to fly another day.