In order to make predictions, your brain must have a model of reality. This model is necessarily much simpler than reality itself. To see why, imagine that you are about to drop a baseball from waist height. Your brain can’t possibly know enough about the atoms composing that baseball and the air around it to simulate what will happen at the atomic level. And even if your brain did have accurate knowledge about the atoms, using information at such a fine a level of detail would be extremely computationally inefficient. Instead, to predict the movement of the ball, your brain uses something closer to the model “when I drop an object, it will fall in a straight line down towards the ground, perhaps rotating slightly as it falls, and bouncing when it lands.” This is an accurate model that is far, far simpler than one that takes into account every atom.

Surprise is the emotion you feel when a prediction made by your brain’s model of what you are going to experience deviates substantially from what you actually experience. If you discover a large mark on your hand that you didn’t know was there, you will feel surprised. Your model of your hand did not match the visual experience produced by the light reflecting off of your hand. If you drop a baseball and it flies towards the ceiling, you will be even more surprised. Your model of what happens when you drop an object was just massively violated.

Our brain is making predictions constantly. Most of the time, these predictions are pretty accurate. When our sensory experience is in line with what our brain expects, it not only does not produce the feeling of surprise, but usually does not even push information about what was just observed into our conscious awareness. Making predictions and then checking these predictions against experience acts as a filtering mechanism. Since we can only keep a very limited amount of information in conscious awareness, it makes sense not to waste this space by filling it with boring stuff that your brain already predicted was going to happen. From the point of view of the survival of our genes, surprising experiences (i.e. ones that your brain mispredicted) are much more useful to reflect on consciously than unsurprising ones.

One thing to note about our brain’s predictions is that they do not correspond to a single, exact pattern of sensory experience. When you are in the forest, and you turn to the left, your brain cannot possibly predict the precise layout of leaves you will now see. But it does expect that you will see leaves, and that they will be (roughly speaking) within a certain range of colors, a certain range of sizes, and so forth. As long as this turns out to be true, you probably won’t even think about the fact that you are now looking at a different pattern of foliage than you were before. But if instead of trees there is a man standing next to you that you did not expect, you’ll immediately become consciously aware of that man.

By taking note of surprise when it occurs, we can learn to have truer beliefs about the world. To see how, imagine that you just heard about the Asch conformity experiments, and you find yourself surprised to learn that most people in the experiment publicly gave the wrong answer to an obvious question just because a large number of other people publicly gave this wrong answer before them. Your surprise signifies an opportunity to know something that you didn’t before, and increase the accuracy of the beliefs in your model of reality.

But how should your model be updated based on this information? A naive updating would be to add a fact to your set of beliefs such as “If 35 people incorrectly claim that one line is bigger than another, then a large percentage of people will publicly claim the same belief as the group.” The problem is that when added in this way, the fact has not truly been incorporated into you web of beliefs. It has merely been glued to the web as a dangling outlier, without altering the web itself to naturally accommodate the new information.

To usefully incorporate surprising pieces of information, ask yourself:

Why did I find this information surprising? This can help you hone in on what parts of your model need updating.

What prior beliefs of mine does this information contradict? Your credence in these prior beliefs should then be lowered.

Which prior beliefs of mine does this information bolster ? Your credence in these prior beliefs should be increased.

? Which beliefs of mine are most natural to tweak so that this fact is no longer surprising? Once the new information no longer seems surprising, it means it has been absorbed into your belief network.

If you find the results of the Asch experiments surprising, it may be that you underestimate what people will be willing to do to avoid looking like an outsider. Or it may be that you underestimate the extent to which people will doubt their own sensory experience when it is contradicted by the opinions of others. In either case, the information you learned from the experiment should alter what you think about things besides what will happen in that precise experimental setup. For instance, this new knowledge may update your views about how cults create agreement among their members. Or it may make you realize that if dissent is not encouraged within an organization, there is a danger that conformity will take over, and the entire group may eventually succumb to obviously wrong, but socially reinforced beliefs.

If after you have updated your model the information you have learned still seems surprising, this indicates that your beliefs need further tweaking to accommodate the new information. You should not be surprised by the same (or very similar) information twice. If a friend cancels plans on you three times in a row, and you didn’t anticipate that they may cancel that third time, you failed to sufficiently process the first two occurrences.

The next time you find yourself feeling surprised, remember that it is a valuable opportunity to update your beliefs.