So far, it’s been a pretty ordinary day. But it’s only 2 p.m. on Friday the 13th, a day that comes around about once a year, and those who suffer from triskaidekaphobia (fear of the number 13) are likely still on the edge of their seats.

Where did this superstition come from? It dates back to ancient Roman times, and some mathematicians explain the numbers behind the yearly cycle. We know that a year will never go by without one Friday the 13th, and the most a year can ever have is three (which is set to happen in 2012).

Historically unlucky events have occurred on this day (earthquakes, mass murders, failed space mission, etc.) but no one really knows for sure why people originally feared the number 13. One story is that in ancient Rome, women who were thought to be witches gathered in groups of 12, and the devil was said to be the 13th.

But nonetheless, as a result, we have numerous superstitions some of which most people don’t even notice.

For instance, the same NatGeo article reports that more than 80 percent of high-rise building don’t have a 13th floor, several airports around the world skip gate 13, and it’s not uncommon for hotels to lack a 13th room.

Also, something like 20 million people in the U.S. have triskaidekaphobia.

Click to sign up for the Advocate's weekly news digest and be the first to know what’s happening in Lakewood/East Dallas.