One lesson a day, spaced reviews that come back when memory fades, a test at the end of each level, a verifiable certificate at the end. Every lesson cites its sources.
Level 1 Foundations
Why your brain misleads you, and why you cannot feel it
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Two speeds of thought
Three riddles almost nobody gets right, and why understanding an illusion is not enough to correct it.
18 min
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The invisible anchor
A number heard thirty seconds earlier shifts your estimate, judges setting a sentence included.
16 min
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What comes to mind
You judge how often things happen by how fast examples come to mind, and the news skews that counter.
16 min
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The coherent story
Confidence measures how coherent the story is, not how good the information is. Thin information, high confidence.
17 min
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Overconfidence, in numbers
Three ranges you set and score yourself. Almost everyone misses more of them than they announced.
17 min
Level 2 Posture
Soldier or scout: what you are looking for when you think
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The soldier and the scout
Two ways to use your intelligence, the same feeling of rigour, and a study where the most numerate split the most.
17 min
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The man who reopened the file
An antisemitic officer discovers the convicted man is innocent. What he does, and what it costs him.
18 min
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Five thought experiments
Five thirty-second tests that bypass introspection, including one that fails in a very instructive way.
18 min
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A number on your certainty
The tally of one famously rigorous man's predictions, and a method for finding your own number.
17 min
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Light identity
Why some beliefs stop being revisable, and how to spot them with a single question.
17 min
Level 3 The language of probability
Saying what you think in numbers, and being scored on it
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The fog of words
In 1951, “serious possibility” meant anywhere from 20 to 80 % to the analysts who had written it together.
17 min
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Cutting the impossible
Answering a question you know nothing about, and seeing which unknown decides everything.
16 min
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Outside first
The base frequency before the details of the case. In the other order, adjusting turns into justifying.
17 min
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The score that forgives nothing
The accounting that makes cowardice and arrogance equally expensive, and that scores your cases.
17 min
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The fox and the hedgehog
Twenty years of study on hundreds of experts: the most televised are the least accurate.
17 min
Level 4 The art of disagreement
Where to look for what the crowd misses, and when to follow it
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The awkward question
A famous interview question, its three false answers, and what makes a real one.
17 min
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Secrets still exist
Where the truths nobody looked for are hiding, and why it is almost never for lack of intelligence.
17 min
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The second level
Being right about a company and making money on it are two different things.
17 min
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What you can't say
Telling a false idea, a forbidden idea and a shocking-and-false idea apart. Beginners confuse the last two.
17 min
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The crowd is often right
Eight hundred guesses at the weight of an ox, and the lesson that keeps this whole level from becoming foolish.
17 min
Level 5 Deciding in the real world
From judgment to decision: judging your choices without lying to yourself
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The decision and the outcome
A pass intercepted twice in a hundred is still a good decision on the day it gets intercepted.
17 min
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Turn the problem over
How would you guarantee failure? The inverted question produces a list, the direct one produces an intention.
16 min
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The premortem
Ten minutes that surface the objections a team would never otherwise put into words.
16 min
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The forces running through you
Show me the incentive, I will show you the outcome. And what happens to a measure once it becomes a target.
17 min
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The complete loop
Six lines written before, reread before you look at the outcome. The whole path fits in there.
17 min
Level 6 The great review
The whole path, retraced in one lesson, before the exam
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Retracing the path
The twenty-five previous lessons in one, before the final exam.
20 min