Probability.

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.

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

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

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

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

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

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

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.

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

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.

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

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