Words are small, but they can be astonishingly powerful. A single short phrase, chosen well, can change the way people think about something in an instant. This is the secret behind advertising: companies spend years searching for a few perfect words — a slogan — because a good one can convince millions of people to trust a product they have never tried. Why do short phrases work so well? For one thing they are easy to remember; for another, a brief, confident message leaves room for our own imagination to fill in the rest, so we end up half-persuading ourselves.

Scientists who study this find that people often trust the written word more than they should, especially when it is bold and unexpected. A claim printed in large letters can feel settled, as though somebody must already have checked it. That is worth knowing, because the same power can be used for good or for ill. The skill that sells a toy can also spread a kind idea or comfort a friend. It can even — as in one famous story — save the life of a small pig, using nothing but two words in a web.

No right or wrong — close the screen and tell someone nearby what happened in this part. Can’t find anyone? Tell yourself out loud. The moment you teach it, you truly understand it.