The infamous day has finally arrived. As many will attest, Friday the 13th is widely accepted in Western culture as being the unluckiest day on the calendar. Still, while everybody knows the day isn’t the most promising one on which to buy a lottery ticket, few know why the day is considered so unlucky.

The superstition is so well-known that scientists have even come up with a word to describe the condition of those with a fear of Friday the 13th: paraskevidekatriaphobia. According to ABC News, the Stress Management Center/Phobia Institute has claimed it afflicts “people with blind, unreasoning fear of this day and date, as opposed to those who have a clear, reasonable fear of not being able to say that word.”

So, now that we’ve established the power the superstition has over the public, it’s time to examine where it actually came from. Unfortunately, nobody has been able to track the exact origin of Friday the 13th’s negative connotation. One of the earliest references to the superstition came in the 19th century when Capt. William Fowler, a Civil War veteran, founded a club devoted to proving superstitions false. The first meeting of the Thirteen Club -- which attracted more U.S. presidents as members than did the Skull and Bones secret society, according to Mental Floss -- got under way Friday, Jan. 13, 1882, at 7:13 p.m. At meetings, the gang would walk under ladders, spill salt and break mirrors in attempts to show the actions would engender no negative consequences.

The next popularization of the myth is associated with Thomas W. Lawson’s 1907 book, appropriately titled “Friday the Thirteenth.” The novel focuses on a ruthless tycoon who uses people’s built-in fear of the date to engineer stock-market booms and busts to his advantage and the disadvantage of his enemies, Time reported. It sold almost 28,000 copies in its first week, LiveScience said.

Although both of these stories explain how the popular superstition got so widespread, neither of them explain how the date became so vilified in the first place. As near as anyone can tell, the cause appears to stems from two separate fears. While there are precious few references to Friday the 13th before the mid-19th century, references to the number 13 and the end of the week being unlucky go back centuries.

In Norse mythology, the number 13 became an unlucky number when 12 gods gathered for dinner, and a 13th showed up to crash the party, as LiveScience noted. The crasher was none other than Loki, the trickster god of mischief: Many will know the character from Tom Hiddleston’s performances in the Marvel Cinematic Universe. Loki took his bow and shot to death Balder the Beautiful, who was the god of joy and gladness. As the story goes, the death brought darkness and mourning to the world and put a stink on having exactly 13 dinner guests forever.

According to National Geographic, the number 13 might have subconsciously been rubbing people the wrong way for years because of its association with the number 12. Numerologists consider 12 a so-called complete number due to things like the 12 months in a calendar year, the 12 signs of the zodiac, the 12 gods of Olympus, the 12 labors of Hercules, the 12 tribes of Israel and the 12 apostles of Jesus. Apparently, it is believed that 13 goes beyond being a complete number, therefore making it clunky and hard to deal with.

As for the stigma surrounding Friday, that’s deeply rooted in Christian traditions. As HowStuffWorks pointed out, many Christians have been wary of Fridays since Jesus was notoriously crucified on a Friday. In addition, many of them interpret the story about the great flood associated with Noah’s ark as beginning on a Friday and the story about the original sin of Adam and Eve as happening on a Friday, as well.

It is believed that these two negative meanings melted together over the years, as superstitious human beings assigned significance to two unlucky things in tandem. Whatever the case, many people to this day refuse to dine with 12 guests, go on a trip, launch a project or even leave the house whenever this combination of day and date pops up.

What will you be doing this Friday the 13th? Tweet your thoughts on the superstition to @TylerMcCarthy.