"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."
Robert A. Heinlein,
The Notebooks of Lazarus Long
In fact there are enough excellent Heinlein quotes it is difficult to pick just one.
There are a ton of them here:
http://en.wikiquote.org/wiki/Robert_A._Heinlein
Tom