The optimist thinks that this is the best of all possible worlds,

The optimist thinks that this is the best of all possible worlds,
and the pessimist knows it.
-- J. Robert Oppenheimer, "Bulletin of Atomic Scientists"

Yet creeds mean very little, Coth answered the dark god, still speaking
almost gently. The optimist proclaims that we live in the best of all
possible worlds; and the pessimist fears this is true.
-- James Cabell, "The Silver Stallion"