This may seem a little bit odd to some of you who have never heard of it, but it's actually true. Tetraphobia is the aversion or fear of number 4 and is a superstition most common in East Asian countries such as China, Japan, Korea and Taiwan. But probably most of you are now thinking "what's wrong with our dearest friend 4 ? ".
The answer is pretty simple... it can be consider a "bad luck sign" because of its sound. In Chinese, the word indicating the "four" (四,pinyin: sì, jyutping, sei), sounds very similar to the word "death" (死, pinyin: sǐ,jyutping, sei), in many forms of spoken Chinese. In the same way, in Japanese and in Korean, words that indicate the four, shi (Japanese) and sa (사, Korean), sound identical to death in both languages.
Particular care is taken to avoid occurrences or allusions to the number 4 during festive holidays, parties, or when a family member is sick, especially in Chinese culture. The numbers 14, 24, etc., are also avoided due to the presence of the digit 4. In these countries, in the buildings, such as hotels, offices, apartments and hospitals, floors with these numbers are often skipped.
On wedding lunches or other convivial occasions the tables numbered 4, 14, 24, etc are often left out, and in many residential complexes, these numbers are replaced with 3A, 13A, 23A, etc. Similarly in the courtyards of siheyuan (traditional Chinese houses) are never planted four trees or four plants in bonsai pots.
Also in a big modern metropolis like Hong Kong, some skyscrapers such as Vision City and The Arch skip all floors from 40 to 49: immediately above the floor 39/F there is 50/F.
Another example of this traditional phobia is the fact that the naming of their military aviation begins with the number 5, as in fighter plane "Shenyang J-5"; in taiwanese and Korean Navy does not use the number 4 when assigning pennant numbers to craft.
In Korea, tetraphobia is less present but the floor number 4 is almost always skipped in hospitals and public buildings. Elsewhere, in the lifts the fourth floor is sometimes labeled "F" (the capital letter of four in English) rather than "4". The numbers that contain multiple occurrences of number 4 (such as 404) are usually avoided, otherwise the value of the property would be compromised.
This traditional superstition is so deeply believed and frightening that when Beijing lost its bid to stage the 2000 Olympic Games, it was speculated that the reason China did not pursue a bid for the following 2004 Games was due to the unpopularity of the number 4 in China. Instead, the city waited another four years, and would eventually host the 2008 Olympic Games, also because the number eight is a lucky number in Chinese culture.
Even in a chinese traditional board game called Go, 4 is the synonymous of “you’re dead !”. in fact a checker surrounded by four opponents dies and is immediately removed from the game. Maybe this is a little far fetched, but I would not be happy to know how many misunderstandings started because of this "issue" they have...