Henry David Thoreau (from Walden ):
To be a philosopher is not merely to have subtle thoughts, nor even to found a school, but so to love wisdom as to live according to its dictates, a life of simplicity, independence, magnanimity, and trust. It is to solve some of the problems of life, not only theoretically, but practically. The success of great scholars and thinkers is commonly a courtier-like success, not kingly, not manly. They make shift to live merely by conformity, practically as their fathers did, and are in no sense the progenitors of a noble race of men.