Today millions of people will experience "triskaidekaphobia"--that is, a fear of the number 13. While this fear derives from the Last Supper, a religious event that is said to have happened more than 2,000 years ago, its effects are still very real.

Sales have been known to drop on this day because people avoid flying and doing business the way they normally would. Some hotels and airports purposefully don't use the number 13, and only fewer than 5 percent of mid- and high-rise residential condo buildings in Manhattan and Brooklyn have a designated 13th floor, according to an analysis by real-estate listings website, CityRealty.

A Gallup poll also reveals that many hotels in Las Vegas, where luck and superstition plays a significant psychological role, do not have 13th floors. Becky Beaton, a licensed psychologist and the founder of The Anxiety & Stress Management Institute, says people's actions surrounding superstitions and gambling can be described as "intermittent reinforcement." The term refers to events that occur only randomly, but enough that they reinforce a desired outcome. So if you have heard of just one bad thing happening on a Friday the 13th, that instance is enough for you to believe the day is bad luck for a long time.

These beliefs cause people to change their actions in varied ways. Some avoid traveling. Others steer clear of scheduling big life events like weddings. And in extreme cases, people decide not to leave their home altogether. "I've definitely seen patients not make huge decisions if it's going to be Friday the 13th," Beaton says. "Like if they're going to close their house on that day, there's no way they would do it."

Industries involved in wedding planning take a huge hit on this day. Tatiana Byron, CEO and founder of New York City event and wedding planning company 4PM Events and Wedding Salon, says Friday the 13th definitely affects business because of people's refusal to travel or purchase major items. Couples on a whole avoid the date, but especially when they have destination weddings and are asking guests to travel.

Byron estimates that the events industry might not have any events at all planned for this day. "If you speak to any average photographer, florist, or venue, Friday and Saturday are their business days," she says. "But Friday the 13th they usually don't have events, [or if they do] very rarely."

Perhaps unsurprisingly, financial markets appear little moved by the date. On the last Friday the 13th, Howard Silverblatt, senior index analyst for S&P, Dow Jones Indices, notes that the S&P 500 closed higher 56 percent of the time when the 13th day of the month fell on a Friday.

The sales loss per the unlucky date stems from the skewed expectations people form and how they let it control their daily habits. Dr. Cynthia Ackrill, a stress expert at wellness consultancy, WellSpark, says people's superstitions suggest an expectation for certain events, akin to a self-fulfilling prophecy. "Superstitions change your story for the day so that changes your perception," Ackrill says. Perceptions can then affect actions, she adds. "It's amazing how our minds bend our worlds." 

So how do you influence people's perceptions so they don't get scared off?

Byron recommends embracing the day with special Friday the 13th promotions and/or offering incentives to those who book and purchase. She also advises business leaders to prepare in advance because she says, "not everyone cares and some can be swayed by value."

Instead of viewing today as completely detrimental to your sales, try changing your perception to think of it as an opportunity to challenge your business, suggests Byron. "Why can't it become like a Black Friday, versus it being a taboo date?"