In Japanese superstition, four is avoided because its pronunciation can mean “death.”
The number is commonly read as shi, while the Japanese word for death is also pronounced shi. This creates a sound-based taboo known as tetraphobia, especially in hospitals, hotels and other settings where people may avoid associations with death.
Japanese also has another pronunciation for four, yon, which does not carry the same ominous meaning. As a result, the superstition is not an absolute ban: people may choose yon in ordinary speech, while shi is avoided in sensitive contexts.
The same sound association appears in parts of China and Korea, where words for four can resemble the word for death. This is different from the Western fear of 13, because the Japanese concern is primarily a homophone-based linguistic superstition.