Descartes' error was separating mind from body and reason from emotion

Damasio names his book after what he considers philosophy's foundational mistake: Descartes' claim that mind and body are separate substances, with rational thought as the pure, disembodied essence of a person, distinct from and superior to the messy machinery of the body and its emotions. This dualism seeped into medicine, psychology, and popular culture, producing the enduring image of the ideal decision-maker as someone who suppresses feeling to think clearly.

Damasio's clinical evidence contradicts this directly: reasoning is not a separate, purified process running independently of bodily and emotional states, but is continuously shaped and informed by them. The brain regions responsible for reasoning and those responsible for regulating body states and generating emotion are deeply interconnected, not walled off from each other.

This reframing has consequences well beyond neuroscience, touching how we design decision-making systems, evaluate leadership, and think about what 'rational' even means.

Takeaway: stop treating emotion as reason's enemy — the two systems evolved together and function together.