The Chinese word for four (四, pinyin: sì, jyutping: sei3), sounds quite similar to the word for death (死, pinyin: sǐ, jyutping: sei2), in many varieties of Chinese. Similarly, the Sino-Japanese, Sino-Korean, and Sino-Vietnamese words for four, shi (し, Japanese), and sa (사, Korean), sound similar or identical to death in each language (see Korean numerals, Japanese numerals, Vietnamese numerals). Tetraphobia is known to occur in Korea and Japan since the two words sound identical, but not at all in Vietnam because they carry different tones (in the case of the word for "four", whether it is the Sino-Vietnamese reading tứ or the more common non-Sino-Vietnamese reading tư, neither sounds like the word for "death" which is tử), and Vietnamese does not use Sino-Vietnamese numerals as often in the first place.
Special care may be taken to avoid occurrences or reminders of the number 4 during everyday life, especially during festive holidays, or when a family member is ill. Mentioning the number 4 around a sick relative is strongly avoided. Giving four of something is strongly discouraged. Elevators in Asia and Asian neighborhoods often skip the 4th floor. Military aircraft and ships also avoid the number 4 (such as the South Korean and Taiwanese navies). April 4 is also considered an exceptionally unlucky day, much like Friday the 13th in the West.
Similarly, 14, 24, 42, etc. are also to be avoided due to the presence of the digit 4 in these numbers. In these countries, these floor numbers are often skipped in buildings, ranging from hotels to offices to apartments, as well as hospitals. Table number 4, 14, 24, 42, etc. are also often left out in wedding dinners or other social gatherings in these countries. In many residential complexes, building block 4, 14, 24 etc. are either omitted or replaced with block 3A, 13A, and 23A. Hospitals are of grave concern and the number 4 is regularly avoided altogether. Tetraphobia can dictate property prices. Neighborhoods have removed four from their street names and become more profitable as a result. In the same way, buildings with multiple fours can suffer price cuts. Four is also avoided in phone numbers, security numbers, business cards, addresses, ID numbers, and other numbers and are considered severe as they are personally attached to the person.
Tetraphobia far surpasses triskaidekaphobia (Western superstitions around the number 13). It even permeates the business world in these regions of Asia.