The number 13 is synonymous with the superstition of bad luck. Many people actually believe that it means bad luck. The number 13 actually has a long history behind it that is more prevalent than one may realize.
The first thing that many people think of when they hear the number 13 is Friday the 13th. There is at least one Friday the 13th in a year, and often there are two, but in 2009 there were 3 - in February, March, and November. Many people feel this day is bad luck and will not do anything that they might think might go wrong; this includes having parties or going to places. The United States looses 800-900 million dollars in business on Friday the 13th because people are too superstitious to travel or go to work. Roughly eight percent of the population is afraid of Friday the 13th. This condition is known as paraskevidekatriaphobia. This fear affects about 17 to 21 million people in the United States. This may all seem ridiculous, but British scientists have found that the number of hospital admissions increases by as much as 52% on Friday the 13th.
The superstition surrounding Friday the 13th is actually the combination of two separate fears: the fear of the number 13, called triskaidekaphobia, and the fear of Friday's. These fears have many religious ties due to historical mishaps that may have occurred on the 13th.
The fear of Friday the 13th may also have to do with people’s fear of the unknown. It is the first number that cannot be enumerated using out 10 finger and two feet. This fear also affects anything that is numbered in sequential order. Sometimes tall buildings will skip the 13th floor and number it as 14 or 12a, or many streets will not label their house 13. There are also instances where a musician may not put a track 13 and may skip to 14. When traveling, you have to be careful because on many airlines, there is no row 13, so if your ticket says row 13, you may not have a seat!
Strangely, the number 13 is very visible in history. Did you know that is you look at $1 bill, you will see it reflected many times - 13 levels in the pyramid, 13 stars, 13 arrows, 13 stripes, 13 leaves, and 13 olives? Another historical element is that there were originally 13 original colonies in America.
The media has picked up on these fears and many movies have 13 on them. Most movies are scary, such as Friday the Thirteenth, Thirteen, Thirteen Ghosts, and Nightmare on the 13th Floor. There are also movies with 13 in the title which aren't scary, such as 13 Going on 30, Apollo 13, and Thirteen Days. In addition to media, books have also implemented the scare factor of the number 13. If you read The Series of Unfortunate Events by Lemony Snicket, you may realize that every book has 13 chapters and there were 13 books in the series.

Many other things have 13 as a part of them as well. In a deck of cards, there are 13 cards in a suit and a baker’s dozen would not be possible without 13. Adding to this is the idea that if the number of letters in your first and last name adds up to 13, you are said to have devil’s luck.

Not everyone shares this fear. For example, many people are born on the 13th consider it to be a lucky day. So whether you believe in the superstition or not, it’s up to you, but if you believe that something bad is going to happen, then it probably will. There is even a suspicion between psychologists that people are more likely to get sick or have an accident on Friday the 13th. Such things happen not because the day is necessarily unlucky, but because people experience a heightened sense of anxiety.