The Demon-Haunted World was incredibly formative for me, and I was around 14 when I first read it. Prior to reading it, I believed wholeheartedly that UFOs were alien spaceships, and despite already being fairly certain I was an atheist, I was still on the fence about ghosts. The most important thing about that book was that it didn't teach me that things I believed weren't true because a distinguished scientist said so; rather it taught me how to decide whether the things I believed were likely to be true, and how to examine why I believed them.

Of course I didn't immediately transform into a perfect 14-year-old skeptic by reading this book (I'm twice that age now and I'm sure I still believe all manner of things that aren't true), but this was the first time I truly realized that I even needed to be skeptical about what I believed.