What can be asserted without evidence can also be dismissed without evidence. — Carl Sagan

What can be asserted without evidence can also be dismissed without evidence.

Author: Carl Sagan

Insight: We live in an age where everyone's an expert, and most of us are drowning in claims—some backed by nothing but confidence and repetition. This idea cuts through all that noise. If someone tells you something without showing their work, you're under no obligation to believe them, no matter how certain they sound or how many people nod along. The sneaky part is recognizing when we ourselves are the ones making claims without evidence. We do this constantly: about why our coworker acted that way, what our partner really meant, or why we'll definitely go to the gym tomorrow. We treat our hunches and feelings like facts, then get frustrated when others don't just accept them. The quote works both directions—it's a permission slip to question others, but also a mirror to examine our own thinking. This matters because the world rewards people who sound sure of themselves, whether they know what they're talking about or not. Learning to ask "where's the evidence?" before accepting either other people's claims or your own assumptions is genuinely powerful. It's not about being cynical; it's about being honest with yourself about what you actually know versus what you're just assuming.

Source: Cosmos, p. 182, 1980