Humans tend to fear things that are potentially dangerous, rather than things that are not threatening. Psychologist Martin Seligman suggests this is because humans?

Psychologist Martin Seligman suggests this is because humans still carry evolutionary traits in them.

Explanation:

Even though there are potentially more dangerous things in a modern society, like the fear of planes or cars, people tend to develop phobias for the less dangerous things like the fear of height or rats, etc. Seligman argues that humans carry these fears since the dawn of species, when these were signaled danger. Phobias to cars and planes are less likely to develop because humans are not biologically primed to develop such fears.