From Oliver Wendell Holmes in The Profession of the Law:
"No man has earned the right to intellectual ambition until he has learned to lay his course by a star which he has never seen — to dig by the divining rod for springs which he may never reach. In saying this, I point to that which will make your study heroic. For I say to you in all sadness of conviction, that to think great thoughts you must be heroes as well as idealists. Only when you have worked alone — when you have felt around you a black gulf of solitude more isolating than that which surrounds the dying man, and in hope and in despair have trusted to your own unshaken will — then only will you have achieved. Thus only can you gain the secret isolated joy of the thinker, who knows that, a hundred years after he is dead and forgotten, men who never heard of him will be moving to the measure of his thought — the subtile rapture of a postponed power, which the world knows not because it has no external trappings, but which to his prophetic vision is more real than that which commands an army."