Dossey traces the fear of 13 to a Norse myth about 12 gods having a dinner party at Valhalla, their heaven. In walked the uninvited 13th guest, the mischievous Loki. Once there, Loki arranged for Hoder, the blind god of darkness, to shoot Balder the Beautiful, the god of joy and gladness, with a mistletoe-tipped arrow.
http://news.nationalgeographic.com/news/2004/02/0212_040212_friday13.html
I love learning about new phobias because I love the names! Triskaidekaphobes are people who fear the 13th. Which is a common superstition among people in America. There are all kinds of superstitions like don't step on a crack or opening an umbrella indoors. These things are good representations of strange behavior. Why do people believe these are true? Who starts these and says this is what will happen to you if you don't follow it? I know that when I was little I believed that if I didn't take a running leap onto my bed that an alligator would reach out from under my bed and grab me. I lived in Northwest Iowa there were no alligators there. Was it something that I had a dream about, or maybe an irrational fear of something under the bed that I represented with alligators? I'm not really sure but I bet that everyone at some time in their life has had a superstition no matter what they say.
I was blown away by the number of people who are truly affected by 'Friday the 13th' and the millions of dollars that are lost on these days. I had never heard these statistics before. I agree with the author that lots of phobias are actually caused by the person themself and that believing in bad luck can actually cause bad luck. However, I also believe that some people are actually 'conditioned' to have phobias... if that makes sense? For example, I myself fear spiders... not to the extent of being arachnophobic, but after getting bit by a spider as a small child, they make me extremely uncomfortable. I believe that my behavior is a result of a painful experience that happened to me. I'm going out on a limb here, but in a way that could be operant conditioning. The consequences of being bit by that spider increased my disliking. And perhaps someone who fears flying once fell off of a ladder and now fears heights because of it? Granted, not everyone's superstitions or phobias stem from a painful experience but I think that is another interesting factor that could be looked into.