The belief in lucky and unlucky days is very old and appears to have been originally taught by the magicians of ancient Chaldea. The natives of Madagascar have since the earliest times believed in lucky and unlucky days of birth, and in previous times if a child was born on what they considered the unlucky day, it would be killed.
The ancient Greeks believed that the 13th day was unlucky for sowing, but favorable for planting. Many early peoples harbored the superstitious belief that it was best to sow seed at the full of the moon. Others maintained that it was best to gather in the harvest when the moon was full. Still others regarded the crescent moon as a fortunate omen. Even today in South Africa, many people consider it unlucky to begin a journey or undertake a work of importance during the last quarter of the moon.
The Romans marked their lucky days with a piece of chalk, their unlucky days with charcoal. From this custom of marking unlucky days with charcoal started the phrase "black-letter day." Today, "black-letter days" are generally ones remembered with regret because of some unfortunate occurrence connected with them.
"Blue Monday" is an old phrase still in general usage. In early days those whose business circumstances forced them to work on Sunday, the official day of rest, were considered entitled to a holiday on Monday. On Monday, therefore, while others were back at work, the people who worked on Sunday had a day of rest. Because the churches throughout Europe were decorated with blue on the first Monday before Lent—which was a holiday or "lazy day" for everyone—the day of rest throughout the rest of the year for the Sunday workers came to be known as "Blue Monday." Although the term is still used, now when people speak of a "Blue Monday," they most often wish to convey that they feel lazy, tired, or would rather be on holiday than at work.
The origin of the superstition concerning Friday is traced by most authorities to the crucifixion of Jesus Christ (c. 6 B.C.E.–c. 30 C.E.) on that day. But some writers advance the theory that Friday is regarded as an unlucky day because, according to ancient tradition, it was on Friday that Adam and Eve partook of the forbidden fruit and were cast out of paradise.
Followers of Islam try to avoid beginning any new enterprise on Wednesdays. For reasons long forgotten, Wednesday is seen as a bad day. Even today, many Muslims avoid even getting their hair cut on that day. And such important occasions as weddings are never scheduled for a Wednesday.
A familiar old rhyme preserves the old superstitions concerning the personalities of various children on various birthdays: "Monday's child is fair of face,/Tuesday's child is full of grace,/Wednesday's child is sour and sad,/Thursday's child is merry and glad,/Friday's child is loving and giving,/Saturday's child must work for a living,/But the child that is born on Sunday/Is blithe and bonny, good and gay."