JUNIOR EDITION for Ages 6+
Decisions: The Science of Thinking Clearly · Book 1

Misjudgment: Why Smart Brains Get Fooled

Why do clever, careful people still make big mistakes?

In this book, you will find out…

When you grow up, you could…

Who is in the story

SiriSiriPuzzle solver. Hates being wrong (at first).
CharlieCharlieAsks one good question — then lets Siri find out.
WarrenWarrenTurns up late. Thinks about a hundred years from now.

Today’s mystery

Why do clever, careful people still make big mistakes?

Look for the clues. Try to guess the answer before Siri does!

Chapter 1

The Wobbly Bridge

🔍 Why would a brand-new bridge wobble?
A brand-new bridge opened over the river. Crowds came to walk across.
A brand-new bridge opened over the river. Crowds came to walk across.
Then the bridge began to swing from side to side! People grabbed the rail.
Then the bridge began to swing from side to side! People grabbed the rail.
Siri wrote one word in her notebook: Why?
Siri wrote one word in her notebook: Why?
SiriIt's brand new. How can it be wrong?
Two days later, the bridge was shut. Siri had a job for Friday. She chose this mystery.
Two days later, the bridge was shut. Siri had a job for Friday. She chose this mystery.
Siri had a guess.
Siri had a guess.
SiriSomebody built it too weak. Cheap steel!
So the engineers tested it again, with two thousand walkers. Siri watched their feet.
So the engineers tested it again, with two thousand walkers. Siri watched their feet.
When a floor moves, people spread their feet to keep their balance. They push.
When a floor moves, people spread their feet to keep their balance. They push.
Each push made the swing bigger. A bigger swing made more pushes!
Each push made the swing bigger. A bigger swing made more pushes!
Siri’s notebook
Not weak! People walking made the bridge swing.
The fix was dampers, bolted underneath to soak up the swing.
The fix was dampers, bolted underneath to soak up the swing.
Charlie found Siri staring at the bridge.
Charlie found Siri staring at the bridge.
SiriSo the engineers made a mistake.
CharlieDid they? Which sum was wrong?
None! Every sum was right. A question was missing.
None! Every sum was right. A question was missing.
SiriHow do you find a question nobody asked?
Chapter 2

The Guess-My-Rule Game

🔍 How do you catch a mistake you can't see?
Charlie wrote three numbers: 2, 4, 6. They followed a secret rule.
Charlie wrote three numbers: 2, 4, 6. They followed a secret rule.
Siri could test any three numbers. He would only say yes or no.
Siri could test any three numbers. He would only say yes or no.
She had it in four seconds.
She had it in four seconds.
SiriEight, ten, twelve. Add two!
CharlieYes. That fits.
She tried more. A hundred, a hundred and two, a hundred and four. Yes. Yes!
She tried more. A hundred, a hundred and two, a hundred and four. Yes. Yes!
Siri said her rule out loud. It was wrong!
Siri said her rule out loud. It was wrong!
She had never tried numbers she expected to fail. Not even once.
She had never tried numbers she expected to fail. Not even once.
The real rule was huge: any three numbers that go up.
The real rule was huge: any three numbers that go up.
SiriOne, two, ninety works too?!
Hunting for yeses felt just like checking. That was the trap.
Hunting for yeses felt just like checking. That was the trap.
SiriIt really felt like checking.
Siri’s notebook
To catch a mistake, try to prove yourself WRONG.
Siri had a new worry. What if grown-ups also ignore a
Siri had a new worry. What if grown-ups also ignore a "no"?
Chapter 3

The Blurry Telescope

🔍 What happens when people ignore a "no"?
A giant telescope flew high above the air to look at stars.
A giant telescope flew high above the air to look at stars.
But the first pictures were blurry. Every star was a smudge.
But the first pictures were blurry. Every star was a smudge.
Siri had a guess.
Siri had a guess.
SiriSomething broke on the way up!
Nothing had broken. But the mirror was smooth, beautiful — and a tiny bit the wrong shape.
Nothing had broken. But the mirror was smooth, beautiful — and a tiny bit the wrong shape.
The cause was a measuring tool with one worn spot.
The cause was a measuring tool with one worn spot.
Two other tools had said the mirror was wrong. Two big
Two other tools had said the mirror was wrong. Two big "no" answers!
But people trusted the main tool. The warnings were put aside.
But people trusted the main tool. The warnings were put aside.
Later, astronauts flew up and gave the telescope its own glasses.
Later, astronauts flew up and gave the telescope its own glasses.
Now it sends back sharp, beautiful pictures.
Now it sends back sharp, beautiful pictures.
SiriThe warning was there all along!
🔎 Clue found!
A "no" answer is a gift. Don't throw it away.
They believed the answer they liked, like Siri did. But why do whole rooms agree?
They believed the answer they liked, like Siri did. But why do whole rooms agree?
Chapter 4

The Wrong Line

🔍 Why would a whole room give a wrong answer?
A card shows three lines. One of them matches the line beside it.
A card shows three lines. One of them matches the line beside it.
People answer out loud, one by one. One person answers last.
People answer out loud, one by one. One person answers last.
The first person picks a line that is too short. So does the next!
The first person picks a line that is too short. So does the next!
Siri had a guess.
Siri had a guess.
SiriThey're just being polite. Nobody believes it.
Alone, on paper, almost everyone picks the right line.
Alone, on paper, almost everyone picks the right line.
But in the group, many people went along with the wrong answer.
But in the group, many people went along with the wrong answer.
Then one change. Just one other person disagrees.
Then one change. Just one other person disagrees.
SiriI bet that helps a lot!
Siri was right! With one friend, most people said the true answer.
Siri was right! With one friend, most people said the true answer.
🔎 Clue found!
One brave voice helps everyone tell the truth.
Charlie asked a harder question.
Charlie asked a harder question.
SiriI'd speak up. Anyone would.
CharlieWhat would it cost to be the only one?
Counting voices is not the same as checking. But can a silly number fool people too?
Counting voices is not the same as checking. But can a silly number fool people too?
Chapter 5

The Spinning Wheel

🔍 Can a random number change your answer?
A wheel with plain coloured parts. It knows nothing at all.
A wheel with plain coloured parts. It knows nothing at all.
Siri was sure the wheel could not matter.
Siri was sure the wheel could not matter.
SiriIt's a wheel. It knows nothing!
But the wheel was set. For half the people it stopped at 10. For half, at 65.
But the wheel was set. For half the people it stopped at 10. For half, at 65.
People who saw 10 guessed low. People who saw 65 guessed much higher!
People who saw 10 guessed low. People who saw 65 guessed much higher!
Same question. Same kind of people. A number from nowhere changed the answer.
Same question. Same kind of people. A number from nowhere changed the answer.
It works like an anchor. Your thinking stays close to where it drops.
It works like an anchor. Your thinking stays close to where it drops.
Then Siri thought of price tags. Somebody picks that first number on purpose.
Then Siri thought of price tags. Somebody picks that first number on purpose.
So Siri made a plan. Decide your own number first.
So Siri made a plan. Decide your own number first.
Siri’s notebook
Pick my own number BEFORE I hear theirs.
The wheel had moved Siri too. So how sure should she ever feel?
The wheel had moved Siri too. So how sure should she ever feel?
Chapter 6

The Driver Survey

🔍 Can almost everyone be better than average?
Ask each driver: are you safer than most drivers here?
Ask each driver: are you safer than most drivers here?
Almost nine in ten said yes!
Almost nine in ten said yes!
Siri checked the sum twice.
Siri checked the sum twice.
SiriImpossible! Nine in ten can't be in the top half.
She was right. Half must be below the middle. That is what middle means.
She was right. Half must be below the middle. That is what middle means.
One more sure step can take a sure person right to the edge.
One more sure step can take a sure person right to the edge.
So Siri wrote her guesses down first, with a date. Then she checked.
So Siri wrote her guesses down first, with a date. Then she checked.
🔎 Clue found!
Feeling sure is a feeling. Being right needs checking.
A page of guesses to mark later. An honest scoreboard! But can luck fool us too?
A page of guesses to mark later. An honest scoreboard! But can luck fool us too?
Chapter 7

The Lucky Dice

🔍 Does praise make people do worse?
Teachers watched new pilots land planes, week after week.
Teachers watched new pilots land planes, week after week.
They said: praise a great landing, and the next one is worse.
They said: praise a great landing, and the next one is worse.
Siri thought about it.
Siri thought about it.
SiriMaybe praise makes people a bit sloppy?
So she tested it on something that can't hear praise. Two dice!
So she tested it on something that can't hear praise. Two dice!
Roll. Write it down. Roll again. Twenty times.
Roll. Write it down. Roll again. Twenty times.
SiriAfter a 12, the next roll will be lower.
She was right. After a 12, the next roll was almost always lower.
She was right. After a 12, the next roll was almost always lower.
Very high rolls are rare. So an ordinary roll usually comes next.
Very high rolls are rare. So an ordinary roll usually comes next.
One sunflower grows extra tall this year.
One sunflower grows extra tall this year.
Next year the row is more even. Nobody did anything!
Next year the row is more even. Nobody did anything!
🔎 Clue found!
Sometimes a pattern is just luck, not a cause.
Siri had six cases now. But what would she say on Friday?
Siri had six cases now. But what would she say on Friday?
Chapter 8

The Long View

🔍 What do you do after a mistake?
Siri pinned all her cases up and drew string between them.
Siri pinned all her cases up and drew string between them.
Every mistake had been made before. So you can look for it!
Every mistake had been made before. So you can look for it!
SiriClever people. Careful people. They still slipped.
But Siri still had one question she could not answer.
But Siri still had one question she could not answer.
Warren listened to all six cases.
Warren listened to all six cases.
SiriHow do I stop making mistakes?
WarrenYou won't. What happens when you make one?
Siri thought about a dam. It is built for more water than anyone expects.
Siri thought about a dam. It is built for more water than anyone expects.
Spare oars are useless every day. Except one day.
Spare oars are useless every day. Except one day.
SiriLeave room to be wrong!
On Friday, Siri stood up with her notebook.
On Friday, Siri stood up with her notebook.
SiriSmart people slip. Here's how we can look for it.
She closed her notebook. Then she opened it again. Somebody got paid in every case. Why?
She closed her notebook. Then she opened it again. Somebody got paid in every case. Why?

All the clues

  1. A "no" answer is a gift. Don't throw it away.
  2. One brave voice helps everyone tell the truth.
  3. Feeling sure is a feeling. Being right needs checking.
  4. Sometimes a pattern is just luck, not a cause.

So… Why do clever, careful people still make big mistakes?

They forget to ask one question. They hunt for "yes". They copy the crowd. They feel sure without checking. Then the clever ones leave room to be wrong.

OmahaIndia Junior · a simpler version of Book 1 for readers aged 6-8