No. 303 · Your own mind · General Thinking
Semmelweis Reflex
We reflexively reject new evidence when accepting it would mean we were wrong.
In the Almanac
“Washing hands in Vienna”, 1847–1865 · “Kodak”, 1975
Both stories in full, three ways to use it and where it misleads.
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Questions
What is Semmelweis Reflex?
The Semmelweis Reflex is our tendency to dismiss new evidence before weighing it, simply because it clashes with what we already believe. It is named after Ignaz Semmelweis, whose handwashing data slashed maternal deaths in the 1840s, yet many doctors rejected it.
How do you use Semmelweis Reflex?
When something contradicts you, pause before dismissing it. Ask whether the evidence is genuinely flawed or whether it just threatens your identity. Cultivate intellectual humility, seek out thoughtful people who disagree with you, and treat being wrong as a step toward being right.
When does Semmelweis Reflex matter?
Semmelweis Reflex is one of the 31 mental models for your own mind, the situations where you ask: Is my own thinking leading me astray? Within that, it belongs to “Seeing what you want to see”, alongside Blind Spot Bias, Cognitive Dissonance and Commitment and Consistency Bias.
What is an example of Semmelweis Reflex?
Two stories show it at work: Washing hands in Vienna (1847–1865) and Kodak (1975). Both are told in full in The Mental Models Daily Almanac, which has two stories for each of its 365 models.
Which mental models are related to Semmelweis Reflex?
Paradigm Shift, Backfire Effect and Generals Fighting the Last War. Semmelweis Reflex itself comes from general thinking.