@Brian G Turner With all due respect, we could move into religious discussions from here, but I do not think we're there. (I do appreciate the gentle reminder instead of a ban hammer. But please slap me, electronically, if I overstep my bounds.)
To me, superstition and religion can be separate. I am just trying to understand how one dinner with Judas evolved into a powerful superstition of western civilization. I'd never thought of it before and the connection does not seem rational to me. But perhaps by definition, superstitions are not completely rational.
After college, I lived in Taiwan for two years. I worked for a school during my first year and for a business during the second. In both cases, my employers supplied my residences. Both were on the seventh floors of apartment buildings, but the second did not have a fourth floor. Many buildings in Chinese culture, especially hotels and hospitals, do not have a fourth floor. In Mandarin Chinese, the number four is pronounced the same as death. So they avoid speaking of living on the death floor.... This is a superstition I can understand.
I can more readily understand ladders and black cats, but tossing salt, knocking on wood, and the number thirteen are incomprehensible to me.
It's probably unfair of me to demand answers here without at least doing some poking around the netweb on my own. So here's a blurb from the PsychicLibrary:
There is a term for a fear of the number 13 triskaidekaphobia, of Greek origin. The term for a fear of Friday the 13th is paraskevidekatriaphobia.
Across many cultures, the belief that the number 13 is evil and brings bad luck is so strong that many hotels, office and apartment buildings do not have or recognize a 13th floor, airports usually do not have a 13th gate and many people stay home on Friday the 13th.
The Chinese and ancient Egyptians believed the number 13 brings good fortune. The Egyptians believed in 12 stages in life toward spiritual enlightenment. The 13th stage was the eternal afterlife. In this sense, death was not a place of fear, but a place of high regard for the afterlife.
One theory about why this negative belief about the number 13 exists is that Judas, who betrayed Jesus, was the 13th person to be seated at the Last Supper.
In 1881, a group of New Yorkers set out to debunk this and all other superstitions and formed a group called the Thirteen Club. Its first meeting took place on Friday the 13th at 8:13 pm and 13 people sat down to dinner in room number 13. To get into the room each guest walked under a ladder and sat down around piles of spilled salt. Needless to say, all of the guests survived. For the next 40 years, Thirteen Clubs cropped up all over the U.S., but then faded from popularity.
Here's a quote from How Stuff Works:
The superstition associated with the number 13 is so common that it even has its very own name, albeit one you probably can't pronounce: triskaidekaphobia. People are so afraid of this seemingly innocent number that the United States economy loses almost a billion dollars in business every time Friday the 13th rolls around. It also explains why more than 80 percent of high-rises don't have a 13th floor: Architects skip straight from 12 to 14 to appease suspicious folks. So how did 13 get its spooky rep? It might date back to a Norse myth: When a 13th guest showed up to a party attended by 12 gods, one of the gods ended up dead, and tremendous destruction followed. The suspicion of the number 13 could also be blamed on Judas, who was the13th guest to make it to the Last Supper, and everyone knows how well that turned out.
History.com says that the Sumerians basic counting system was based on 12, not 10. Thus 12 was a number of completion and perfection, making 13 unbalanced and awkward.
On topic, I still agree with Teresa.
