Why Friday the 13th Is Unlucky

The Unluckiest Day of All - The astute reader will have observed that while we have thus far insinuated any number of intriguing connections between events, practices and beliefs attributed to ancient cultures and the superstitious fear of Fridays and the number 13, we have yet to happen upon an explanation of how, why or when these separate strands of folklore converged — if that is indeed what happened — to mark Friday the 13th as the unluckiest day of all.
There's a very simple reason for that — nobody really knows, though various explanations have been proposed.

Bad FridayLEGEND HAS IT: Never change your bed on Friday; it will bring bad dreams. Don't start a trip on Friday or you will have misfortune. If you cut your nails on Friday, you cut them for sorrow. Ships that set sail on a Friday will have bad luck – as in the tale of H.M.S. Friday . One hundred years ago, the British government sought to quell once and for all the widespread superstition among seamen that setting sail on Fridays was unlucky. A special ship was commissioned, named "H.M.S. Friday." They laid her keel on a Friday, launched her on a Friday, selected her crew on a Friday and hired a man named Jim Friday to be her captain. To top it off, H.M.S. Friday embarked on her maiden voyage on a Friday, and was never seen or heard from again.

Some say Friday's bad reputation goes all the way back to the Garden of Eden.
It was on a Friday, supposedly, that Eve tempted Adam with the forbidden fruit. Adam bit, as we all learned in Sunday School, and they were both ejected from Paradise. Tradition also holds that the Great Flood began on a Friday; God tongue-tied the builders of the Tower of Babel on a Friday; the Temple of Solomon was destroyed on a Friday; and, of course, Friday was the day of the week on which Christ was crucified. It is therefore a day of penance for Christians.
In pagan Rome, Friday was execution day (later Hangman's Day in Britain), but in other pre-Christian cultures it was the sabbath, a day of worship, so those who indulged in secular or self-interested activities on that day could not expect to receive blessings from the gods — which may explain the lingering taboo on embarking on journeys or starting important projects on Fridays.

To complicate matters, these pagan associations were not lost on the early Church, which went to great lengths to suppress them. If Friday was a holy day for heathens, the Church fathers felt, it must not be so for Christians — thus it became known in the Middle Ages as the "Witches' Sabbath," and thereby hangs another tale.

13: The Devil's DozenLEGEND HAS IT: If 13 people sit down to dinner together, all will die within the year. The Turks so disliked the number 13 that it was practically expunged from their vocabulary (Brewer, 1894). Many cities do not have a 13th Street or a 13th Avenue. Many buildings don't have a 13th floor. If you have 13 letters in your name, you will have the devil's luck (Jack the Ripper, Charles Manson, Jeffrey Dahmer, Theodore Bundy and Albert De Salvo all have 13 letters in their names). There are 13 witches in a coven.

Though no one can say for sure when and why human beings first associated the number 13 with misfortune, the belief is assumed to be quite old, and there exist any number of theories — all of which have been called into question at one time or another, I should point out — purporting to trace its origins to antiquity and beyond. It has been proposed, for example, that fears surrounding the number 13 are as ancient as the act of counting. Primitive man had only his 10 fingers and two feet to represent units, this explanation goes, so he could count no higher than 12. What lay beyond that — 13 — was an impenetrable mystery to our prehistoric forebears, hence an object of superstition.