We all have our bad days, but Friday the 13th is the worst of all in many western cultures. Is it just superstition or is it really unlucky when the 13th day of the month falls on a Friday? Friday and the number 13 are associated with bad luck separately. In the Bible, Friday was the day Christ was crucified, and it was the day for execution in pagan Rome. Some religious scholars believe that Eve fed Adam the forbidden fruit on a Friday and it was also the day when the great flood began. It is said that a century ago, the British government sought to eradicate the superstition among sailors that setting sail on a Friday was unlucky by naming a ship H.M.S. Friday as well as hiring a man named Jim Friday to be captain. The ship embarked on her maiden voyage on a Friday and it - as you might have guessed - disappeared. The number 13 is also synonymous with bad luck. One reason is that there were 13 people at the biblical Last Supper, and the traitor Judas was the 13th guest. Also, according to Norse myth, 12 gods were invited to a banquet, and the arrival of the 13th, uninvited guest - Loki the god of mischief - resulted in the death of Balder the Beautiful, the god of joy and happiness. The number is so disliked that many western cities and buildings do not have a 13th street or 13th floor. Some historians have said the number was purposely smeared by founders of patriarchal religions in the early days of civilisation because it represented femininity, corresponding to the 13 lunar cycles in a year. As the solar calendar - following the rise of patriarchal civilisation - gradually replaced the lunar calendar, the number 13 became a symbol of bad luck. So how and when did Friday and the number 13 join hands to become one super unlucky day? There are many theories regarding the origin of Black Friday, but none of them is universally accepted. A prominent one - recently presented as fact in the novel The Da Vinci Code - holds that the day became cursed about 700 years ago when the Catholic Church ordered the persecution of the Order of the Knights Templar. The Knights had become too powerful, threatening the rule of the monarchy and the pope. It is said that on the infamous October 13, 1307 - a Friday - mass arrests were carried out during a raid and several thousand knights and priests of the order were charged with heresy and blasphemy. Many of them were either tortured to death or burned at the stake in the years that followed their arrest. People who suffer from a severe case of paraskevidekatriaphobia - a fear of Friday the 13th - avoid getting out of bed today. Others also avoid travelling, dining out or moving into a new flat. Additional reporting by Young Post interns Jeremy Cheung and Jason Ng Not-to-do list: Don't change your bed on Friday or you will have bd dreams. Don't cut your nails on Friday sorrow will befallyou. Avoid having 13 people for dinner or everyone will die within the year. Avoid having 13 letters (e.g. Jack the Ripper, Charles Manson) in your name or you will have the devil's luck.