Carl Sagan’s famous line was popularized in Broca’s Brain in 1979 and then reached an even wider audience through Cosmos in 1980. That’s when I first heard it. I was 15 years old when Cosmos aired which was a seminal moment in my life.
The deeper idea is older—David Hume used a similar principle when discussing miracles—but Sagan gave it its modern scientific voice. In context, the quote is not anti-wonder. It is anti-carelessness. It says the more a claim challenges what we already know about reality, the more evidence it needs before we raise our confidence in it.
For Sagan, and me, science did not kill spirituality; it deepened it. Stars, evolution, atoms, life, death, and cosmic scale were sources of humility and reverence. But his awe stayed disciplined. If someone says meditation brings peace, modest evidence may be enough because the claim fits ordinary human experience. If someone says meditation opens a portal to a hidden realm, the evidence burden rises. Sagan’s spirituality was wonder with calibration: reality first, awe second, certainty only when earned.
The Why Truth Requires Reality article explains why truth is alignment with reality, and belief is confidence in that alignment. Calibration is the process of adjusting confidence to the kind and quality of support behind a claim. Empirical claims answer to observation and testing. Rational claims answer to logic and coherence. Speculative claims may remain meaningful, but they should be held with humility. Disproven claims should be released as truth. This is how spirituality stays honest: not by rejecting wonder, but by ranking confidence properly when wonder reaches into the material world.