What is the hasty generalization fallacy?

Drawing a sweeping conclusion about a whole population from a sample that's far too small to support it.

The pattern: a small (or unrepresentative) sample S is taken from population P, and a broad conclusion about P is drawn from it. It fails because small samples rarely mirror the whole — they're too easily skewed by chance or by the few cases you happened to see.

A visitor arrives in a new country, has one rude taxi driver, and concludes "people here are all rude."

One encounter can't characterise millions of people. The cure is a sample large and varied enough to be representative; the more diverse the population, the bigger the sample needs to be. (The related biased generalization uses a sample that's the wrong shape — like polling gun owners to gauge everyone's view on gun control.)

Tip: Watch for "I met one… so they're all…" — that leap from a handful to "all" is the tell.