It’s easier to forego temptation than it is to stop after only a bit.
For example, it’s easier to not have any ice cream at all, than it is to eat just the “recommended portion.”
In these situations inertia serves us.
If we’re standing still in relation to something (for example, the ice cream in the freezer), then it’s easier to not have some than it is to stop eating after one spoonful.
At least it is for me . . . .