In his book The Social Animal, David Brooks summarizes vast amounts of social science research by stating that "information programs alone are not very effective in changing behavior." He writes:

Both reason and will are obviously important in making moral decisions and exercising self-control. But neither of these character models has proven very effective. You can tell people not to eat the French fry. You can give pamphlets about the risks of obesity. You can deliver sermons urging them to exercise self-control and not eat the fry. And in their nonhungry state, most people will vow not to eat it. But when their hungry self arises, their well-intentioned self fades, and they eat the French fry. Most diets fail because the conscious forces of reason and will are simply not powerful enough to consistently subdue unconscious urges.

The evidence suggests reason and will are like muscles, and not particularly powerful muscles. In some cases and in the right circumstances, they can resist temptation and control the impulses. But in many cases they are too weak to impose self-discipline by themselves. In many cases self-delusion takes control.