The Book of Fears evolved from an ongoing curiosity of people's aversions and obsessions. What makes a person afraid? When does that fear become a phobia?  Included in the series are some well-known fears that a lot of people face on a day-to-day basis, such as achluophobia (fear of darkness), hydrophobia (fear of water), and then some not-so-well-known worries such as somniphobia (fear of sleep).