A world of ideas.

A host who knows the answer changes what an open door tells you.

A small room contains far more possible pairs than people.

More observations can stabilize an average without making the next outcome predictable.

Small repeated changes build on everything that came before.

Adding one more input can produce less extra output than the one before.

Choosing one useful thing means giving up another useful thing.

Money already spent can pull a decision away from what happens next.

An initial number can keep pulling an estimate toward itself.

Tests that agree with a theory may leave its strongest rivals untouched.

An immediate reward can outweigh a larger future one—and reverse an earlier plan.

Memory fades, and the timing of review changes what remains available later.

Shared resources depend on both individual demand and the rules people build together.

A tempting individual move can leave both players worse off.

Local preferences can produce a larger pattern that nobody explicitly chose.

Tiny differences in starting conditions can grow into very different trajectories.

The shape of a response determines whether variation helps or hurts.

Separate a protected reserve from a small, explicitly risky allocation.

The right to act without an obligation changes the downside of uncertainty.

Who receives the upside—and who bears the loss—can change a decision.

A long reassuring history can miss the mechanism that ends it.

A valuable shared goal can require confidence that others will join.

Each side wants the other to yield, but mutual escalation is costly.

A predictable choice can be exploited even when neither pure choice is best.

A shared convention can help people choose the same place without talking.

A contribution can benefit the whole group while costing the contributor.

An offer can be profitable and still be rejected.

A negotiated split depends on what each side can get without a deal.

Paying the second-highest bid changes the incentive to report your value.

The highest estimate may be the one with the largest upward error.

When buyers cannot observe quality, good products can leave the market.

A trend inside every group can reverse when the groups are pooled.

Known odds and unknown odds can feel different even when their midpoint matches.

Two pairs of lotteries can expose tension in how we value certainty.

People can follow earlier actions even when their own clue disagrees.

A shared project succeeds only after enough people contribute.

The first person can grow a shared pie but cannot force a fair return.

Passing grows the pot, but each player can take it first.

Everyone benefits if one person acts, but each hopes someone else will.

Try to predict what others will predict, not a number's intrinsic value.

Two sellers compete for customers spread along one street.

Stopping too early and searching forever can both lose the best candidate.

Trying an uncertain option can teach you something, even when another seems better now.

The final missing item can take much longer than the first few.

A streak can feel like it makes the opposite result due, even when trials are independent.

A random arrival is more likely to land in a long gap than a short one.

Leading digits in scale-spanning measurements are often far from uniform.

A stricter threshold reduces false alarms but can miss real signals.

A fair binary event carries more uncertainty than one that almost always repeats.

Repeating a bit can overcome some errors but uses extra capacity.

An extra shortcut can make selfish routing slower for everyone.

A part that cannot be sped up limits the gain from adding more workers.

More items in a stable process usually means a longer time spent inside it.

Small customer changes can become larger swings in upstream orders.

A more efficient tool can increase total resource use if demand expands enough.

A small fraction can account for a large share when values have a heavy tail.

A ranked item can appear roughly in inverse proportion to its rank.

Contact and recovery rates change the shape of an outbreak in a closed population.

Growth slows as a population approaches a finite capacity.

Two interacting populations can rise and fall out of phase.

A very small population may struggle to recover even when resources are available.

A small change in visible adoption can trigger a larger collective shift.

Equivalent outcomes can feel different when described as gains or losses.

Owning an item can change the price at which someone is willing to give it up.

An inferior third option can change how two original options are compared.

A remembered experience may emphasize its strongest moment and its ending.

A project can take longer than the inside-view estimate suggests.

Early adopters and imitation can create an S-shaped adoption curve.

Moving toward the middle can win more nearby voters in a simple one-dimensional election.

If everyone expects a quiet venue, the venue may become crowded.

Spending more effort raises your chance of winning but everyone pays their effort cost.

For some things, the longer they have lasted, the longer they may last.

Extreme events can be more common—and more consequential—than we expect.

Having an edge is one thing. Knowing how much to bet is another.

Even a favorable game can end badly when your resources are finite.

A convincing story can make us forget how rare something was to begin with.

An extraordinary result is often followed by something more ordinary.

When a measure becomes a target, it can stop being a good measure.

The stories we can see may hide the evidence we need most.

A small number of outcomes can account for a very large share of the whole.

Losing something can feel larger than gaining the very same thing.

Some things become more useful when more people use them.

When someone acts on your behalf, whose interests are they serving?

The chance of crossing a boundary from which you cannot continue.

When does an average across many worlds describe one journey through time?