Take a look at any fantasy or science fiction novel, and you will find a few fears that drive all the characters to some sort of action.
Fear of death – This is the most common motivator. The hero or villain fears their own or a loved one’s death, so they fight, conquer, or search for the MacGuffin that could prevent it. Nearly every fantasy and sci-fi novel has some fear of death. It’s why thieves evade being captured, assassins fight their target’s guards, and soldiers combat the enemy.
Fear of creepy crawlies – Snakes, spiders, cockroaches, rats, and other creepy crawlies are terrifying to many people. There are many phobies related to contact with these animals. Many sci-fi novels, in particular, use this fear to create alien races that are instinctively perceived as evil. After all, saying something has a snake-like appearance or a “rat face” is immediately “bad”.
Fear of the dark – There is an instinctive fear of the dark, because darkness hides potential threats. Assassins like the Hunter of Voramis use the darkness as cover, then jump out at their victims. Darkness can also hide magical threats, monsters, and more. The absence of visual input allows the mind to run wild with potential dangers. It’s why scenes where the main character creeps through the dark are so much scarier than scenes set in bright daylight. And it’s why so many “scary places” tend to be dark.
Fear of disfigurement and dismemberment – Many heroes try to escape torture before their sword hands are chopped off, or someone reveals information before the person torturing them removes an eye or their tongue. The fear of disfigurement stems from the natural reaction of disgust to anything abnormal or asymmetric, as well as the fear of being alone (no one could love someone so disfigured, the brain tells you). The fear of dismemberment stems from a fear of losing a part of one’s self, as well as a fear of being vulnerable (no legs to run away from danger, no hands to hold weapons).
Fear of the unusual – Things that are commonplace/well-known can become utterly terrifying when they change. For example, scary clowns, your best friends turning into zombies or vampires, and statues coming to life to kill you (a la Dr. Who’s Weeping Angels). The mind rebels against the changes made to the thing we’re so familiar with. That change from known to unknown can be scarier than things that are visibly monstrous.
Fear of being alone – Fear of being alone stems from a fear of vulnerability, which is the primal fear that we, the weakest member of the herd, will be picked off by a predator. Fear of being alone is also tied to our sense of self-worth and self-esteem. It’s easy for the psyche to make the jump from “no one loves me” to “I’m not worth loving”. That loss of self-value is another of the most primal fears that govern all human action.