It starts when you step out of the shower, dripping, and you have no towel.

And then . . . checks bounce, your suit rips, the boss yells, your kid's sick, dinner burns, your mate has a headache, your cat is pregnant and the dog has fleas.

Friday the 13th is supposed to be One of Those Days when you're better off staying in bed. The superstition has its roots in ancient beliefs that numbers have a mystical significance, with those between 1 and 13 holding peculiar power.

Three was one of the luckiest numbers -- believed sacred for its association with the Holy Trinity -- and 13 the unluckiest. There were 13 at the Last Supper; witch-covens contained 13 people; ancient Romans considered 13 a symbol of death and destruction.

The 13th of the month was considered a bad day to embark on any new enterprise -- doubly so if Friday (a religious day on which work was taboo).

To be born on Friday the 13th, however, was considered lucky.

Other modern-day superstitions rooted in ancient beliefs:

Rabbit's Foot: Because of the rabbit's prolific tendencies, it was revered among primitives, who considered birth a sign of the god's favor. The foot was the most sacred part, since it was most often in contact with the earth -- the source of life.

Four-leaf clover: Clover, particularly the rare four-leaf, was one of the "anti-witch" plants which protected humans and animals from evil spells.

Horseshoes: Belief in its goodluck power stems from its lunar shape -- roughly resembling the horned new moon -- and because it's made of iron, regarded as a "magic" metal. (When finding a horseshoe, you should, of course, pick it up, spit on it, make a wish, throw it over the left shoulder and walk away without looking back. Or take it home and nail it over the door.)

Breaking a Mirror: The image in a reflective surface was thought to be a person's soul. Shattering the mirror harmed the soul.

Spilling Salt: Since it does not decay and can preserve other things from spoiling, salt was considered a symbol of eternity and protection against evil. Some believed that for every grain of salt spilled, a tear must be shed.

Knocking Wood: Speaking of any fortunate circumstance or hoped-for event was thought to tempt evil spirits. The sound of knocking wood kept the demons from hearing