This is a very old Chinese practice, going back at least to the early Confucians with their ``five relationships'' and ``three sage kings.'' Groups of five were particularly favored, and from the Han on a system of correspondences was elaborated between the five elements, directions (including the center), colors, flavors, animals, virtues, etc., etc. (See Needham and Tuan's Passing Strange and Wonderful for details.) The closest European analogues I can think of are from the Catholic Church: four doctors, four cardinal and three theological virtues, seven deadly sins.