Rules of Thumb
Heuristics are just that: rules of thumb. They're based on experiences and produce almost immediate decisions—but not perfect ones. One heuristic is the availability heuristic. It affects our judgment based on what information most readily comes to mind. For example, in choosing where to eat, we might pick the restaurant whose commercial we just saw, simply because that information is first available to memory retrieval.
We also see the availability heuristic when estimating probabilities. In making travel plans, for example, people sometimes avoid airplanes for fear of terrorist attacks. We may travel by car instead, even though a fatal car accident might be thousands of times more likely than a hijacked plane. But because terrorist attacks, due to their emotional weight, come to mind most readily, we irrationally decide against air travel. The decision is quick—we don't think deeply about it—but, as you can see, it does trade off accuracy for speed.
Pictures on the Wall
However, if given these two: a program where 2/3 of people die, guaranteed, or a program where there's a chance everyone lives (33%) and a chance everyone dies (66%), most people chose the second. Why? Apparently, we naturally play it safe with gains (1/3 lives saved, guaranteed) but more willingly gamble to avoid losses (2/3 dead). Even though both choices are identical in gains and losses, their framing—the focus on lives saved or lives lost—affected participants' judgments.
A number of other heuristics influence our decisions each day, too: the representativeness heuristic, the recognition heuristic, anchoring (or the focusing effect), and a bunch more.
Fool Me Twice
Most of the time, heuristics are the perfect decision-making tool; they're the ideal balance of fast and accurate. But there are times when greater accuracy is necessary. Heuristics, as you saw above, aren't perfect. In those times, be wary to rely on them, even if the solution they produce "feels" better—for example, when voting or when safety is at risk. But knowing how your brain works is the best way to use it, since you can optimize its many features. Happy thinking!
And that's heuristics in a bathroom break.