Both optimists and pessimists contribute to our society. The optimist invents the airplane and the pessimist the parachute.

The quip frames optimism and pessimism as complementary forces in technological and social progress. “Optimists” are cast as the drivers of bold invention—willing to imagine flight and take the risks needed to build an airplane. “Pessimists,” by contrast, are portrayed not as naysayers but as prudent anticipators of failure who design safeguards, here symbolized by the parachute. The joke’s deeper point is that innovation needs both temperaments: visionary ambition to push boundaries and skeptical foresight to mitigate harm. It also hints at a mature view of pessimism as a form of responsibility—planning for worst cases so that daring projects can be attempted with fewer catastrophic consequences.