四 is considered unlucky because it sounds like 死 (sǐ, death). Many buildings in China skip the 4th floor (and 14th, 24th, etc.), similar to how some Western buildings skip the 13th floor. Phone numbers and addresses with 四 are avoided.
culture
Despite the superstition, 四 appears in many positive traditional phrases: 四面八方 (all directions), 四季如春 (four seasons like spring, meaning pleasant year-round).
