Well, that depends. It's a mistake to assume that a fanciful concept can't be treated with realism. It's actually possible to handle something fantastic with sufficient verisimilitude and care that it feels plausible. Richard Matheson has said that the key is to have just one fanciful element and treat everything around it in as naturalistic and credible a way as possible. And there have been good attempts in fiction to approach fanciful phenomena within the context of otherwise plausible science to make them feel more convincing -- like when hard-SF author Larry Niven was tasked with creating a new "series bible" for Green Lantern comics back in the '80s. Chris Claremont and John Byrne managed to do a fair job making the X-Men's powers seem like they had at least one foot in real science, like having Nightcrawler's teleportation be subject to conservation of momentum (so that if he were falling, he couldn't just teleport safely to the ground because he'd arrive with the same velocity).