Because I was born on a Friday the 13th, and that’s pretty awesome.
The only time I was ever given flack for that was in fifth grade when my actual birthday was a Friday the 13th, because when you’re eleven kids are still generally superstitious but I was super mature and told them to shut up and that my mom was bringing in brownies so whatever.
Anyway! This is what I figure Fluttershy is like every Friday the 13th. While I was finishing this off I realized I was a little surprised that Ponies hasn’t done an episode devoted to Fluttershy’s superstitiousness, or anypony’s superstitiousness (the Pinkie Sense doesn’t count).