I've read recently that, contrary to common sense, willpower is a limited resource and can only get you so far. Running out of willpower is called "ego depletion." How much does this limit us as human beings? If I were a heavy heroine user for several years, and hadn't used in 18 hours, might it be physically impossible for me to resist a readily available supply in certain circumstances? Or are humans just beings of unlimited potential? Is it true that you can accomplish ANYTHING as long as you're smart enough and physically capable? Or is that just an unrealistic fantasy? This may or may not be synonymous with the question "is there free will?"