For American English speakers, that's fear of the number 13. And how appropriate is it that I have four friends with birthdays today.
I pointed out that a 13th floor doesn't diminish property values in pricey markets. Nor is the floor by pure essence of labeling and weaker than the 12th or 14th floors. There were also 13 people at the Last Supper.
There could be a scientific explanation to bad things happening on Fridays that fall on the 13th: There is nothing to fear than fear itself. That is, fear made you fail that quiz. Or just utter non-preparation. Or this- lighting bug repelant on fire to create a fireball for your Friday 13th ritual. Bad idea. The can could explode. Just an example. Make the day more unlucky. (Someone did post a live picture of the bonfire tonight).