Mathematically it's the same as the difference between one and two, but from a philosophical point of view it is much larger. A quitting smoker knows the difference.
The willpower they wield when they've not smoked for half a day is small, but once that day is over, the willpower grows, grows to the point where, if lucky,
days turn to weeks and weeks turn to months.
However, there is always that thought in the back of their head.
*I can have just one, I'll start again tomorrow.*
But when they cave, the cycle starts over. They are no longer a non-smoker, they are a smoker who happened to not smoke for three months.
That willpower is now back at zero and they need to start again; just one cigarette.
*It's the same with everything.*
What stops you from doing something bad?
Is it the illegality of it?
Is it the fact you'd get caught?
What stops you from turning those little thoughts, everyone has, into reality?
The willpower it takes to resist your darkest thoughts, your morals; those are the biggest hurdles.
Do you let yourself think about how to get away with murder? Letting your mind wander, conjuring up the perfect crime.
*What if you succeeded?* Came up with a fool-proof scenario, in your mind, picked a mark; you even reason with yourself why that person you picked deserves it.
How much willpower do you need to turn your plan into reality?
And if you do succeed? How much willpower will you need for the next one?
The difference between one and two is much smaller, trust me.