So today is Friday the 13th. And if you're thinking "big deal", you're right. It is a big deal. Such a big deal that nearly $1 billion worth of commerce won't happen across the United States alone, because people are afraid to fly, travel, and shop.

But you're not one of those people, right?

Actually, I'd bet you are. Maybe you're not a paraskevidekatriaphobe. That's the fancy Greek term for people who fear Friday the 13th. Paraskevi is the Greek word for Friday, and dekatria is how Greeks say 13. Phobe, as you might have guessed, relates to phobia. But I'll bet you do things every single day because - know it or not - you are a little bit superstitious.

Many cultures around the world today and throughout history 'have had a thing' for the number 13 and the day Friday falling on the same time. Call it superstition, call it urban legend, call it fact. Whichever way you look at it, there are plenty of sides to this story.

To the ancient Egyptians, life unfolded in stages - 12 in this life and a 13th beyond, thought to be the eternal afterlife. The number 13 therefore symbolized death. The Holy Bible tells us there were exactly 13 present at the Last Supper. One of the dinner guests betrayed Jesus Christ, setting the stage for the Crucifixion. Did I mention the Crucifixion took place on a Friday?

When you yawned this morning (after getting up on the right side of the bed and starting your day off on the right foot), did you carefully cover your mouth? Probably so. It's what we do to be polite. But there's more to it than this--people used to think that your soul would rush out of your body if you issued an unprotected yawn. And the same goes for sneezing. You may say "Bless you!" to be a nice person. But what you're actually doing is carrying on a tradition apparently started by the Roman emperor Tiberius. According to one legend, Tiberius would ride in his chariot blessing anyone who sneezed, because a deadly disease at the time, in its early phases, caused sneezing. The more blessings were passed around, the less likely people were to die - or so the thinking went. This same thinking continued in Europe in the Middle Ages, when people were dying of bubonic plague. Saying "Bless you!" isn't so silly, of course. Combine it with the cover-the-mouth-and-protect-your-soul rule, and you are much less likely to spread nasty germs.

But Friday the 13th is special. It combines Friday, considered an unlucky day by many, with the number 13, which has long been considered bad news. Maybe you never thought of Friday as unlucky. Friday's often payday for working stiffs. It's the start of the weekend. There's even that "TGIF" restaurant that serves great food (if you want to tempt fate and clog your arteries, that is). Friday is also the Muslim Sabbath and is the day for religious gatherings.

But Friday also carries negative connotations. For starters, Eve is rumored to have given Adam the apple on a Friday. Talk about a snack that's spelled eternal heartburn, even in Disney films. What fruit knocked out Snow White? Right. The apple. The really amusing thing, however, is that the old adage "An apple a day keeps the doctor away" has actually been shown to be true.

And the number 13 has been feared for a long time, too. So much, that about 90 percent of elevators don't have a button for the 13th floor. This is simply because the buildings they are in don't have a 13th floor at all. And the fear is historic: A Norse myth has it that a great dinner party with 12 guests was ruined when a 13th crashed the event and killed the God of Joy and Gladness.

So, it's no wonder that we sometimes make a big deal out of Friday the 13th, even today, when we're steeped in science and technology, and know a great deal about how the world works.

We usually think superstitious people just don't know any better, but that's pretty snobby of us. Superstitions are so common that sometimes we don't even recognize them for what they are.

Thankfully, I do. Touchwood to that.