Scientists experiment with cloning, stem cell therapy and robotic prosthetics because they envision the human condition extending in a very real framework beyond the parameters and provisions that most would call realistic. One in which a person with cirrhosis or heart disease need only make a withdrawal from their refrigerated safe deposit box at the organ bank, and have their doctor pencil them in for a two o'clock transplant. One that sees amputees fitted with new limbs that respond to neurological commands as adeptly as real flesh and bone, and genes that are conducive to crippling disease de-bugged like substandard programming.
By that same token, fantasy writers want to show the human race what it could, and would do were there enchanted portholes to carry us from one world to another, invisible beings walking beside us since the beginning of time who finally revealed that they're here and pissed off, a fountain of youth to which one must make a Faustian bargain before drinking, eagles to ride, sandworms and sea serpents to flee or harness.
We stretch the elastic human spirit with an unnatural pull, and see what weaknesses and strengths poke out through the threads. We provide our characters a palette of colors that can't be found on our earthly plane, and see if they paint something that can.
And sooner or later every dragon or flesh-eating monster displays beneath its mythical shell the worries and misery towards which we're constantly darting eyes over our shoulders, while every "Dark Lord" seeking a hidden weapon to dominate his enemies becomes a world leader in a crisp tailored suit with his finger hovering over the button. The battles our heroes wage against them, whether ending in victory or defeat, can enrich us here with new tactics we may never before have considered.
My protagonist is born with supernatural abilities, and, repressing them his whole life throughout ridicule and isolation, he becomes hopelessly reliant upon an old treasure that promises all the strength he'll ever need. But, the more he accomplishes, the erratic surge of his inner power conflicts with this dependency, culminating in a final, crushing decision he has to make between the two, with his life in the balance.
Fantasy is what enabled me to build my story's hero, with all his wounds and aspirations, in all his tumultuous relationships with humans and beasts alike, around this question: If you had to decide between all the power in the world, and all the power in you... which would you choose?