[W]hen you get past the age where you’re capable of believing there’s something carnivorous and hairy under the bed, you don't then lose your capacity for fear. The monsters go, and in their place, lucky you, you get to start imagining real calamities: losing your parents in a car wreck, becoming destitute, having someone you love turn on you, or doing something so shocking that the community ostracizes you.Adult Fears are about the things mature, well-adjusted adults generally are concerned about, as opposed to supernatural or far-fetched fears: the safety of their children, the safety of their neighborhood, the fidelity of their spouse, the loyalty of their friends and coworkers, being able to pay their bills, etc. Rule of Scary is needed to get from concern to real fear, but Willing Suspension of Disbelief must be maintained for effect. To an adult (especially one with family), kids being preyed upon by pedophiles or sociopaths is scarier than kids being preyed upon by a Xenomorph. Outliving your children in general might be the worst fear of this kind. The audience reaction is still to be scared, but this trope plays down the shock factor of more fantastical horror and plays up the relative realism of more mundane threats. Can have political purposes as well as entertaining ones.
— Alyx Dellamonica, Twilight vs. Flowers in the Attic: Sick Sex Smackdown, Eighties Style