Childermas, or Holy Innocents Day, commemorates the slaughter of the children by the orders of Herod the Great after he was visited by the Magi following the star to the birthplace of the infant Jesus. Because of the horrific associations of the day, it is said to be bad luck to start on a project on this day.
Massacre of the Innocents - Wikipedia
Liturgical Year: Holy Innocents Day
Feasts and Festivals: Holy Innocents