AThe average adult is thought to make around 35,000 decisions every day. Most of them are too small to register. Which shoe to put on first, whether to take a second cup of coffee, which way to walk to the bus stop. A few, however, shape careers, relationships and finances for years to come, and for most of human history these were assumed to be the product of careful thought. A person weighed the available options, considered what each would lead to, and chose the most reasonable one. Modern psychology has taken this picture apart almost completely, and what it has put in its place is stranger than the old story, and a good deal less flattering.

BThe change began in the 1970s with the work of two Israeli psychologists, Daniel Kahneman and Amos Tversky. Their research showed that people lean heavily on mental shortcuts, known as heuristics, whenever a choice involves any real complexity. These shortcuts are not faults in the system. They are the system. The brain is faced at every moment with more information than it can possibly weigh, and it copes by recognising patterns instead of running calculations. Most of the time this works well. The cost is a recurring pattern of errors that the two researchers called cognitive biases. What made this finding so uncomfortable was the suggestion that such errors are not occasional slips but a natural consequence of ordinary mental functioning. Even experts who had spent decades training their judgement turned out to fall into the same traps as everyone else, and often without noticing.

COne of the best known of these biases is the anchoring effect. When asked to estimate a number, people are pulled toward whatever figure they happened to see first, even when the figure has nothing to do with the question. In one well known experiment, participants were asked to write down the last two digits of their social security number, and then to estimate the prices of various items. Those whose digits were higher gave higher estimates, although the connection between the two was plainly nonsense. What is most striking about the effect is how stubborn it is. Even participants told exactly what to expect showed almost no ability to resist the pull of the initial figure. Understanding that a trap exists and stepping around it when it appears are two entirely different things.

DTime pressure makes all of this worse, but not always in the ways people expect. When a decision has to be made quickly, the brain leans even harder on its shortcuts, and the average quality of the choice tends to drop. Yet in some kinds of work, fast decisions are better than slow ones. Veteran firefighters, for instance, have been shown to reach sounder conclusions mid-crisis than when afforded the opportunity to sit and deliberate. Researchers describe this as recognition primed decision making. The expert matches the situation in front of them against thousands of cases stored in memory, and acts on what the recognition tells them. In settings of this kind, stopping to think can do more harm than good. It introduces hesitation where the instinct was already correct.

EFor people without that depth of experience, the picture is very different. A novice under pressure usually performs poorly, falling back on whichever option looks most obvious rather than the one careful thought would have chosen. This matters in fields like medicine and finance, where junior staff are routinely asked to make decisions their training has not really prepared them for. Certain bodies have begun placing junior staff inside high-pressure simulations, on the principle that the instinct seasoned practitioners rely on cannot develop without sustained confrontation with demanding conditions, even manufactured ones.

FThe idea that feeling and sound reasoning pull against each other has deep roots in Western thought. What neuroscience has established over recent decades tells a fundamentally different story. Patients who have suffered damage to the parts of the brain that handle emotion, while keeping their thinking skills intact, turn out to be remarkably bad at making decisions. Such patients can list the advantages and disadvantages of any option in great detail, but they cannot bring themselves to choose. Without emotional weight attached to the outcomes, every option feels roughly the same, and they slip into a kind of paralysis. The lesson is that feeling does not get in the way of reason. It makes reason possible. Emotion provides the quiet ranking system that lets the brain decide which option matters more, and without it, even the cleanest analysis collapses.

GSo what separates a good decision maker from a bad one? The research points in directions most people would not guess. Confidence in your own judgement is a poor sign of accuracy. If anything, the most certain decision makers tend to be a little less reliable than those who hold their views more loosely. Searching out evidence that argues against your preferred answer, rather than evidence that supports it, separates strong decision makers from weak ones more clearly than any test of intelligence does. And experience helps less than people assume. It only sharpens judgement when honest feedback comes with it. Without feedback, repeated decisions in the same field do not refine anything. They only deepen the habits the person already had. The skilled decision maker, on this account, is not the one who feels most certain. It is the one who has learned to mistrust the feeling of certainty itself.