Chinese astrology signs consist of 12 different animals. They repeat themselves on a 12 year cycle. The selection of these animals came about as a race direct by the gods from one river bank to another.
According to legend, 12 animals lined up and could not decide who should start the first year. The gods in their wisdom believed that the Chinese astrology signs should be started by the animal they reached the opposite bank first.
While conceivably the ox should've finished the race first. The cunning rat and snuck onto the ox back at the beginning of the race and jumped off just before the ox reached the other side of the river. This is why the rat starts the Chinese astrology signs every 12 years.
Today, Chinese astrology signs are used on a regular basis in Fortune telling, farmers, calendars, best dates for weddings, and best hours by dates.