Maybe you refuse to open an umbrella inside your house or walk under a ladder that’s on a sidewalk. These are superstitions, or a belief that something bad will happen even if there’s no reason to think that it will. One big superstition in the United States is that Friday the 13th is an unlucky day. Happening up to three times a year depending on the calendar, the day seems to make people more careful or avoid things they usually aren’t afraid to do. Of course, no one can prove that more misfortune takes place on Friday the 13th. We just tend to notice it more if bad things happen on that day. But if Friday the 13th is only a superstition, why do people actually believe in it? It’s hard to know exactly when Friday the 13th became thought of as unlucky, but it likely comes from the Christian religion. For example, in the Bible, Judas—a person who is said to have betrayed Jesus—was the 13th guest at the Last Supper. Also in the Bible, many unfortunate things happened on Fridays. So it made sense that people who read the Bible got nervous around Friday the 13th. It’s also possible that 13 is considered “cursed” because it’s the number after 12, which many people see as a number that completes things. Think about it—12 months are in a year, 12 inches in a foot, 12 pairs of ribs in a body, etc. So it’s possible the number 13 makes people uneasy because it causes them to think about the unknown—beyond the number 12. In other countries, Friday the 13th isn’t unlucky. For instance, in Spain, Tuesday the 13th is considered the day to dread. And in Italy, people fear the 17th day of the any month. Why? It is because the Roman numeral XVII (17) can be rearranged to spell “VIXI,” which means “my life is over” in Latin. But, like in the United States, no one can prove that more terrible things occur on those days, either. People who are super afraid on Friday the 13th might have condition called triskaidekaphobia, which is a fear of the number 13. For most people, being afraid of Friday the 13th is just a superstition, something that we can have fun pretending to fear because we know there’s really nothing to fear.