What is the meaning of the following quote from Ender's Game?
"I am not a happy man, Ender. Humanity does not ask us to be happy. It merely asks us to be brilliant on its behalf. Survival first, then happiness as we can manage it."
This quote comes from Mazer Rackham, who is explaining his life's philosophy to Ender. In Rackham's view, society demands excellence from its citizens, and does not care, at an individual level, if they survive with soul and mental integrity intact. Instead, the individual must fight for his own survival and then make his own happiness with whatever is left over; society will not take any action to ensure the happiness of its citizens without their direct action and deliberate intent.
"Survival first, then happiness as we can manage it."
(Card, Ender's Game, Google Books)
However, Rackham also knows that sometimes terrible sacrifices are necessary for the survival of the human race, and so the happiness of an individual is sometimes of secondary importance; it is more important, when the stakes are so high, to sacrifice as much as possible to win. If there is a chance for happiness later, it will come not from the society, but from an individual's choices and actions.