heuristic
A heuristic is a mental shortcut — a rule of thumb your brain reaches for to get a fast, good-enough answer without grinding through every detail. Faced with a wall of choices, you don't weigh each one; you go with the option that's most familiar, or the price that ends in .99, or the restaurant with the longest line. It's the difference between sprinting down a path you already know and surveying the whole forest first.
Heuristics matter because thinking is expensive and life is fast. These shortcuts let you cross a busy street, read a stranger's mood, or pick a checkout lane in a heartbeat — and most of the time they serve you beautifully. They are not laziness; they are the cleverness of a mind that has learned what usually works.
But the same shortcut that usually wins can quietly misfire. Judge how likely something is by how easily examples spring to mind, and you'll fear plane crashes more than car rides — even though the car is far deadlier. That predictable failure is a bias. The common misconception is that a heuristic is simply a mistake; really, it's a mostly-right rule whose occasional wrong turns are the price of its speed.
Asked which is more common, words starting with "k" or words with "k" as the third letter, most people say the first — because such words come to mind more easily. In fact, the third-letter words are far more numerous.
The availability heuristic: we judge frequency by how easily examples come to mind.
The word comes from the Greek heuriskō, "I find" — the same root as Archimedes' cry of "Eureka!" ("I've found it!"). Psychologists Daniel Kahneman and Amos Tversky put heuristics at the center of how the mind judges, showing in the 1970s how these handy shortcuts give rise to systematic biases.