We all had our own superstitions growing up.

Sometimes it was a specific pair of pajamas that you were certain would bring a snow day the next morning, or maybe it was a Sergei Fedorov jersey that you refused to wash because you wore it during every Stanley Cup playoff game of the 1997-98 season. Maybe you’ve washed that jersey at some point over the years. Maybe you shouldn’t have.

According to the Stress Management Center and Phobia Institute, up to 21 million people in the United States fear Friday the 13th, making it the most feared day in history. It is estimated that up to $900 million is lost on this day because citizens are too afraid to go out and engage.

Why are people afraid of this date? While it’s unclear how this date became so well-known as an unlucky day, a common assumption is that many cultures consider 12 to be a lucky or complete number, and to go beyond 12, to get to 13, is to go too far. There are 12 months in a year; 12 signs of the zodiac; 12 tribes of Israel; Jesus had 12 disciples; 12 imams; 12 gods of Olympus; 12 doughnuts in a dozen; the human body has 12 cranial nerves; 12 pitches in an octave; 12 men have walked on the moon; 12 Angry Men is a great movie — and it still holds up, 60 years later.

Costa Concordia

The Costa Concordia was a cruise ship that sailed for seven years until its fatal sinking on Friday, January 13, 2012.

The cruise ship was on the first leg of a cruise around the Mediterranean when it struck a rock formation after deviating from its planned route. More than 30 people died as a result, 32 passengers and one salvage worker two years after the sinking. New safety regulations have since been introduced to prevent accidents, at the federal level, internationally and by Costa Concordia’s parent company.

Siachen conflict

The Siachen Glacier lies between India and Pakistan, with both countries claiming ownership of the region. After nearly 40 years of head-to-head negotiations, the conflict reached a climax on Friday, April 13, 1984, beginning a war that is technically still ongoing after 36 years.

More than 2,000 people have died on the world’s highest battlefield, 20,000 feet above sea level. It is estimated that 97 percent of the casualties were due to weather, avalanches and lack of oxygen, rather than the actual fighting.

Although a ceasefire came into effect in 2003, the two countries maintain 150 outposts on the glacier, including the world’s highest telephone booth and helicopter pad. The lower air pressure at high altitude has led India to develop an advanced helicopter suitable for the task.

Kitty Genovese

The murder of Kitty Genovese has been a staple of lectures on ethics and psychology for more than 50 years.

She was born and raised in Brooklyn and remained in the city after her parents moved to Connecticut after her mother witnessed a murder on the streets of New York City.

On Friday, March 13, 1964, Genovese was followed home from work and stabbed to death outside her apartment complex. Her cries for help were reportedly ignored by the residents of the complex who overlooked the fatal attack, leading to the bystander effect, a social phenomenon in which people are less likely to help in times of need if others are present, which is taught in nearly every psychology class in the country

The truth behind the real-life murder is a bit different than the sensationalized version that has become known in popular culture. While no one doubts that the murder took place, the details behind the visibility of the attack and the apathy of New York City associated with the witnesses are not believed to be entirely accurate. The New York Times, whose front-page story on the case captured the media’s attention in 1964, recently called its original article “flawed,” “grossly exaggerated,” and that the inaccurate accounts “took on a life of their own.”

It is thought that the bystander effect in times of crisis can be avoided by singling out one person and explicitly demanding that he/she receive help.

Tupac Shakur

On September 7, 1996, influential hip-hop artist Tupac Shakur was shot four times from a passing car in Las Vegas. The attack was reportedly in response to a fight Shakur was involved in earlier that evening.

One of the bullets pierced Shakur’s right lung, causing Shakur to be placed on a ventilator at the hospital and later into a medically induced coma. He eventually died of respiratory failure following surgical removal of his damaged lung on Friday, September 13.

Paris attacks November 2015

The deadliest attack on French soil since World War II was a series of coordinated terrorist attacks in the city of Paris and the suburb of Saint-Denis on Friday, November 13, 2015.

Although multiple groups claimed responsibility for the attacks, then-French President François Hollande announced that ISIS was to blame, and the attack’s organizer was killed in a raid four days later. Muslim leaders around the world condemned the attacks, and new security regulations were instituted around the world in the hope of preventing future attacks.

Is Friday the 13th actually an unlucky day?

Research and statistics have not shown that bad situations occur more often on Friday the 13th, and that the human tendency to favor or interpret information in a way that confirms what we already believe, commonly known as confirmation bias, is to blame. While many bad incidents have happened on the superstitious day, it is easier for us to see them as connected and not look at the amount of bad events that happen on literally every other day of the year.

There were also some good things that happened on this date. President Lyndon B. Johnson signed Executive Order 11375, which prohibited sex discrimination in the federal workforce, on Friday, October 13, 1967. Nintendo released the hugely successful Super Mario Bros. video game for the NES on Friday, September 13, 1985, popularizing one of the most recognizable characters in media. Black Sabbath’s influential self-titled debut album, widely considered the first of the metal genre, was released on Friday, February 13, 1970. More than one person won lottery tickets on this unlucky day.

Is the day truly unlucky? It’s hard to say definitively, given the amount of data and history behind the day, and we’re not saying that the good things about it outweigh the atrocities that took place.

Stay safe. If you are concerned, make an effort not to walk under ladders, avoid black cats and Please leave that Fedorov shirt unwashed this year.