Man has been called a rational being, but rationality is a matter of choice... Man has to be a man-by choice; he has to hold his life as a value-by choice; he has to learn to sustain it-by choice; he has to discover the values it requires and practice his virtues by choice. A code of values accepted by choice is a code of morality.

Atlas Shrugged (ed. E P Dutton, 1957)