Avoid walking under ladders, don̢۪t cross a black cat, don̢۪t open an umbrella indoors, don̢۪t spill salt, and don̢۪t break a mirror.

Why?

Because it̢۪s Friday the Thirteenth, and to some, it̢۪s the most unlucky day of the year.

According to Donald Dossey, founder of the Stress Management Center and Phobia Institute in Asheville, N.C., “It’s been estimated that $800 or $900 million is lost in business on this day because people will not fly or do business [in the United States] they would normally do.”

Dossey estimates that the phobia affects 17 to 21 million people in the U.S.

Paraskevidekatriaphobics are people who are irrationally afraid of the date.

Superstitions don̢۪t seem to affect students on campus. They still go about their daily routines when Friday the Thirteenth rolls around.

Health and rehabilitation sciences major Becky Williams said she doesn̢۪t believe in superstitions.

“I recognize it’s Friday the Thirteenth but I still go out,â€Â Williams said.

One of the reasons people believe the number 13 to be unlucky dates back to the Last Supper where Judas, the one who betrayed Jesus, was the 13th guest.

During the time of the Last Supper, witches in Rome were said to have gathered in groups of 12 and the 13th was considered the devil.

Another explanation of the significance of the number 13 derives from a Norse myth about 12 gods who held a dinner party in their heaven, Valhalla. The uninvited mischievous Loki was the 13th guest to walk in the room and he had arranged for the blind god of darkness, Hodi, to shoot the god of joy and gladness, Balder the Beautiful, with a mistletoe-tipped arrow.

When Balder died the entire Earth became dark and the whole Earth mourned. Since then, the number has become threatening.

According to Dossey, the majority of high-rises don̢۪t have a thirteenth floor, many airports don̢۪t have a thirteenth gate, and it isn̢۪t uncommon for hotels and hospitals to not have a room 13.

The superstition of walking under ladders has been considered blasphemous since the early days of Christianity. The number three was seen as holy because of the Trinity (the Father, the Son, and the Holy Spirit), therefore the triangle was also seen as holy. A ladder leaning up against a wall looked like a triangle, and therefore resembled the Trinity. Walking underneath the ladder would break the Trinity, which could invite unwanted hangings and witch trials.

A black cat crossing one̢۪s path can be unlucky however it̢۪s a mystery exactly where the superstition originated. Black cats were known to hang around with witches. Some cats just send people on edge because they̢۪re very quiet and sneaky.

The breaking of a mirror could damage a soul. The mirror represents not only appearance but one̢۪s soul. The mirror will take revenge of the breaker̢۪s negligence and the mirror breaker will get seven years bad luck.

Criminology major Charlie Naurath also said he̢۪s always aware of Friday the Thirteenth.

“Friday the thirteenth happens on a month that starts with a Sunday,â€Â Naurath said.

In 2009, the months of February, March and November began on a Sunday.

Naurath gives some Friday the thirteenth advice, “watch out for guys with chainsaws.â€Â