Something struck me when I was riding the elevator in my new building—there is a 13th floor.
In the US, there is a superstition about the number 13. I actually had to google “why,” as I just knew it as fact.
According to Wikipedia
The number 13 is considered an unlucky number in some countries. The end of the Mayan calendar’s 13th Baktun was superstitiously feared as a harbinger of the apocalyptic 2012 phenomenon. Fear of the number 13 has a specifically recognized phobia, Triskaidekaphobia, a word coined in 1911. The superstitious sufferers of triskaidekaphobia try to avoid bad luck by keeping away from anything numbered or labelled thirteen. As a result, companies and manufacturers use another way of numbering or labelling to avoid the number, with hotels and tall buildings being conspicuous examples (thirteenth floor). It’s also considered unlucky to have thirteen guests at a table. Friday the 13th has been considered an unlucky day. 
There are a number of theories as to why the number thirteen became associated with bad luck, but none of them have been accepted as likely.
The Last Supper: At Jesus Christ’s last supper, there were thirteen people around the table, counting Christ and the twelve apostles. Some believe this is unlucky because one of those thirteen, Judas Iscariot, was the betrayer of Jesus Christ.
Full moons: A year with 13 full moons instead of 12 posed problems for the monks in charge of the calendars. “This was considered a very unfortunate circumstance, especially by the monks who had charge of the calendar of thirteen months for that year, and it upset the regular arrangement of church festivals. For this reason thirteen came to be considered an unlucky number.” However, a typical century has about 37 years that have 13 full moons, compared to 63 years with 12 full moons, and typically every third or fourth year has 13 full moons.
There’s also a whole thing around Friday the 13th, which includes the whole horror movie franchise.
So what’s my point?
Most buildings in the US don’t have a 13th floor. This includes most hotels I’ve worked at in departments such as Front Office, Reservations, and the Night Audit.
Less than 10 percent of Manhattan condominiums with 13 or more stories actually label a floor with the dreaded number, said Gabby Warshawer, director of research at data and listings company CityRealty. That’s an estimate based on 650 mid- and high-rise buildings that have filed condo declarations with New York City since 2003, including luxury towers going up right now, such as 53W53 and 225 W. 57th Street. source
So there you go, the reason for my surprise that my building has a thirteenth floor.