
Japan is filled with such superstitions. While some are modern urban legends, many come from the animistic roots of Japan's religious beliefs. The many (millions of) gods and evil spirits in nature are capricious and mischievous. They must be appeased or driven away lest they bring death or misfortune to oneself.
Many superstitions surround the fear of death and suffering. The numbers four and nine are unlucky because they are pronounced in the same way as death (shi) and suffering (ku). Hospitals avoid the use of these numbers for rooms and floors. You'll also never find a set of four dishes in Japan. Plateware comes in sets of three or five.