Why is 7 an unlucky number?

The number seven is almost universally thought to be important, usually lucky. It stands for the victory of spirit over matter. Among the Hebrews, seven was the perfect number and denoted completeness. Derived from this, the whole Christian church is symbolized in the Book of Revelation by seven candlesticks, and the perfect power of the Lamb is denoted by seven horns. The use of the number was also frequent among the Greeks. The seventh son of a seventh son was in Britain believed to have psychic or magical powers. In a person's life, there was supposed to be a seven-year cycle. The number seven is associated with the planet Neptune.