Sheep are good-natured, patient and trusting. As sociable herd animals, according to a study, they are able to remember at least 50 faces of fellow sheep. Sheep can live up to 20 years. Across the planet, they are kept for their wool, an indispensable product in the fashion world. The wool of white sheep is preferred. This is the origin of the idiom 'black sheep', whose wool is less valued by industry.