Why people fear the number thirteen

Look at how much is built around twelve: months in a year, hours on a clock face, zodiac signs, a dozen in trade, twelve inches in a foot. The reason is simple: twelve divides by two, three, four, and six. It is easy to split into equal parts - handy for counting and trading.

Thirteen divides only by itself and one. It arrives right after a complete set and becomes extra: a thirteenth month, a thirteenth hour, a thirteenth guest at a table set for twelve. Not a "bad" number, but an awkward one - one that has nowhere to fit.

If the number itself were the issue, people would fear it everywhere. But each culture picks its own unlucky number: usually one that disrupts a familiar count or sounds like an unpleasant word. In Italy, it is seventeen; in China, Japan, and Korea, it is four, which sounds almost like the word "death."

The best-known story is the Last Supper: thirteen sit at the table, and the thirteenth, Judas, betrays. A similar tale is told about a feast of the gods in Norse myths, where Loki arrives uninvited and Baldr dies afterward. But in the myths themselves, no one counts the guests: Loki was made the thirteenth in 19th-century retellings.

Friday became linked to the number late. For a long time, Friday and thirteen were considered unlucky separately; together, they become noticeable in the 19th century, and the 1907 novel "Friday, the Thirteenth," followed later by films, bound them together for good. The arrest of the Templars fell on Friday, October 13, 1307, but it was linked to the origin of the superstition much later.

Developers often skip a floor number: after twelve comes fourteen. Some airlines skip row thirteen too. It is not the owners' belief, but a business calculation: a place with that number is harder to sell. The superstition sustains itself: you see that the floor is missing and conclude there must be something wrong with the number.

Whether the thirteenth brings misfortune has been tested more than once, and the data conflict. A small British study from 1993 found more hospital admissions after accidents on Friday the 13th, but the authors themselves warned that the sample was small. Larger analyses of insurance data find no difference, and sometimes show fewer accidents: some people drive more carefully that day.