Seeing a black cat crossing your path used to mean you would have good fortune, but the introduction of European customs and superstitions reversed that meaning.
Now a black cat crossing your path can only bring bad luck, especially if it crosses from left to right.
It's quite likely that today's superstition is a Western cultural import. In Greek mythology, Zeus’s wife Hera punished her maid Galinthias for impeding the birth of Hercules, transforming her as a black cat. Galinthias later became an assistant to the witchcraft goddess Hecate, and black cats have been tainted ever since.
A cat is a cat, whatever its colour, but black is often associated with dark evil, hiding in the shadows.
The simple Christian ritual "sign of the cross" includes touching your left shoulder before your right, which symbolises Christ carrying us from the left, evil side of life, to righteousness on the right-hand side of God. Hence, the black cat is from the evil side.
However, some Christian Churches, such as East Orthodox, cross right to left, which asks for Christ's love to overcome the evil we bear, or to bless and to protect us from evil.
So does the cat's direction depend on its religious affiliation? And when you approach a cat crossing your path, if you turn round, left becomes right and right becomes left.
The direction of the cat doesn't seem so important.
For most people, seeing a black cat crossing their path is not an everyday occurrence, and probably less frequent that the number of times we have bad luck.
What is the black-cat-crossing : bad-luck-incidence ratio for you?