“It is most important in creative science not to give up. If you are an optimist you will be willing to "try" more than if you are a pessimist.”

“Sometimes it's not the optimist you need, but another pessimist to walk beside you.”

“Don't ever become a pessimist, Ira; a pessimist is correct oftener than an optimist, but an optimist has more fun--and neither can stop the march of events.”

“[…] You see, you are an optimist and live on hope. I am a pessimist and live on experience.”

“To the optimist, pessimists are neurotic; to the pessimist, optimists are deluded.”

“: According to different points of view. To the pessimist: Enemies are everywhere, waiting to ambush you. For the optimist: friends are everywhere, waiting to embrace you.”

“I'd rather be an optimist and a fool than a pessimist and right.”

“I'd rather be optimistic and wrong; than pessimistic and right.”

“It is largely because the free-thinkers, as a school, have hardly made up their minds whether they want to be more optimist or more pessimist than Christianity that their small but sincere movement has failed.”

“Both optimists and pessimists contribute to society. The optimist invents the aeroplane, the pessimist the parachute.”