When you have worn out your shoes, the strength of the sole leather has passed into the fibre of your body. I measure your health by the number of shoes and hats and clothes you have worn out. He is the richest man who pays the largest debt to his shoemaker.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.