All Else Equal: Making Better Decisions Ep70 "The Science Behind Why We Don’t Just Say What We Mean" with Psychologist Steven Pinker - Part 2
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Jan 7, 2026 
In this engaging discussion, Steven Pinker, an acclaimed experimental psychologist and Harvard professor, dives into his latest book, exploring the intricacies of common knowledge. He reveals how common knowledge influences human behavior and financial markets, relating it to speculative trading. Pinker cleverly navigates the pitfalls of mutual knowledge, the psychology behind irrational trading, and the delicate balance of free speech in academic settings. Expect intriguing insights into how collective understanding shapes our actions and societal norms.
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Public Announcement Changes Behavior
- Public announcements create common knowledge that changes behavior compared with private warnings.
- Steven Pinker shows tenants act differently when everyone knows everyone knows a rule is needed.
Limits Of Iterated Reasoning
- People can reliably reason only a few levels deep in mutual knowledge.
- Pinker argues most minds struggle past three or four iterations of "you know that I know."
Spinach-On-Teeth Thought Experiment
- Three psychologists with visible spinach remove it only after a public announcement is repeated three times.
- The iterative reasoning shows how common knowledge at level N triggers action by exactly N people.