In large cities , however , because many make demands on each trade , one alone is enough to support a man , and often less than one : for instance one man makes shoes for men , another for women , there are places even where one man earns a living just by mending shoes , another by cutting them out , another just by sewing the uppers together , while there is another who performs none of these operations but assembles the parts , Of necessity , he who pursues a very specialised task will do it best . '' In large cities , however , because many make demands on each trade , one alone is enough to support a man , and often less than one : for instance one man makes shoes for men , another for women , there are places even where one man earns a living just by mending shoes , another by cutting them out , another just by sewing the uppers together , while there is another who performs none of these operations but assembles the parts , Of necessity , he who pursues a very specialized task will do it best . ''