Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away.
Source: Terre des Hommes (Wind, Sand and Stars), Antoine de Saint-Exupery, 1939
Genuine and primary-sourced. Original French, from the chapter on the airplane: 'Il semble que la perfection soit atteinte non quand il n'y a plus rien a ajouter, mais quand il n'y a plus rien a retrancher.' The English here is a standard faithful rendering. Note the author name should carry the accent: Antoine de Saint-Exupery -> Saint-Exupery (Saint-Exupéry).