Today is Friday the 13th, a traditionally unlucky day on the calendar. Interestingly, there's no particular logic behind why there are superstitions surrounding the day, though there are several theories, the most convincing of which is that it's actually a mash-up of two different superstitions. 13 is a naturally unlucky number because in numerology, the number 12 is considered perfect (while 13 is prime and "unnatural"). In some cultures, Friday is considered an unlucky day, dating back centuries (Jesus Christ was crucified on a Friday, making it something of a cursed day). Friday also has negative connotations in Norse traditions.
In the modern era, Friday the 13th has mostly been associated with the film series of the same name (about a sometimes supernatural mass murderer named Jason Voorhees) and a handful of natural disasters that happened to occur on the day (including the 1972 plane crash that inspired the film "Alive").
Though any evidence pointing to Friday the 13th being unlucky doesn't stop people from picking up an extra bit of paranoia ever time it rolls around. Luckily, there are music videos to help. Plenty of songs and clips have embraced the idea of luck (and, more importantly, keeping bad luck away). Madonna sang about her "Lucky Star," Jagged Edge declared one woman their "Lucky Charm" and Ace of Base celebrated "Lucky Love." And Fridays don't end poorly for the Cure (as long as "Friday I'm in Love" is to be believed).