On December 13, 2019 it is Friday the 13th again. In Western civilizations people believe this is an unlucky day, which means that accidents and hoodoos tend to occur on that day. Those Fridays are a combination of the death day of Jesus Christ and the unlucky number 13.
It has been tried often to understand what made such a superstition about Friday the 13th develop. One explanation is that both on their own, Fridays and the number 13 had been symbolizing bad luck for a long time. That must have led to superstitious people awaiting an enormous disaster for the date when the two hoodoos would come together. This idea must have settled down so deeply in the Western cultures that nowadays even people who would neither actually fear Fridays nor the number 13 would still be frightened and believe in bad luck for days when the 13th day of a month would be a Friday.
There are even people who suffer of so called triskaidekaphobia, which is the pathological fear of Black Fridays. Those people would go so far and not fix any meetings or appointments on a Friday the 13th. They also would not go on vacation, or leave the house at all.
But it would not always need a Friday the 13th to make people believe in bad luck. In many other countries it is other days, which are known as hoodoos. In China and Japan for example, the number four is known as an unlucky number. That is because of the pronunciation of that word, which is quiet similar to that of the word for “death”. People in Spain, Greece and Latin America (except for Brazil) also consider the number 13 as a hoodoo, but only in case of it is on a Monday. However, in Italy Fridays are supposed to be unlucky days, too, but only on the 17th of a month.