Here's two of my favourites:
Manners are a sensitive awareness of the feelings of others. If you have that awareness, you have good manners, no matter what fork you use.
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, and die gallantly.
Specialization is for insects.
"”Robert A. Heinlein