Brains are complex structures whose precise organization and connectivity makes us who we are. Who would have thought, then, that so much could be learned about human cognition, longevity, energetic cost and even evolution by turning brains into soup? In this talk, Suzana Herculano-Houzel tells the story of how she suspected that a number of "facts" about the human brain were really just intuitions, and set out to collect actual data on how many neurons different brains are made of, and why that matters.