Hamlet may have said that human beings are noble in reason and infinite in faculty, but in reality — as four decades of experiments in cognitive psychology have shown — our minds are very finite, and far from noble. Knowing the limits of our minds can help us to make better reasoners.
Almost all of those limits start with a peculiar fact about human memory: although we are pretty good at storing information in our brains, we are pretty poor at retrieving that information. We can recognize photos from our high school yearbooks decades later—yet still find it impossible to remember what we had for breakfast yesterday. Faulty memories have been known to lead to erroneous eyewitness testimony (and false imprisonment), to marital friction (in the form of overlooked anniversaries), and even death (skydivers, for example have been known to forget to pull their ripcords — accounting, by one estimate, for approximately 6% of skydiving fatalities).
Computer memory is much more better than human memory because early computer scientists discovered a trick that evolution never did: organizing information according by assigning every memory to a sort of master map, in which each bit of information that is to be stored is assigned a specific, uniquely identifiable location in the computer's memory vaults. Human beings, in contrast. appear to lack such master memory maps, and instead retrieve information in far more haphazard fashion, by using clues (or cues) to what it's looking for, rather than knowing in advance where in the brain a given memory lies.
In consequence, our memories cannot be searched as systematically or as reliably as those of us a computer (or internet database). Instead, human memories are deeply subject to context. Scuba divers, for example, are better at remembering the words they study underwater when they are tested underwater (relative to when they were a tested on land), even if the words have nothing to do with the sea.
Sometimes this sensitivity to context is useful. We are better able to remember what we know about cooking when we are in the kitchen than when we are skiing, and vice versa.
But it also comes at a cost: when we need to remember something in a situation other than the one in which it was stored, it's often hard to retrieve it. One of the biggest challenges in education, for example, is to get children to take what they learn in school and apply it to real world situations, in part because context-driven memory means that what is learned in school tends to stay in school.
Perhaps the most dire consequence is that human beings tend almost invariably to be better at remembering evidence that is consistent with their beliefs than evidence that might disconfirm them. When two people disagree, it is often because their prior beliefs lead them to remember (or focus on) different bits of evidence. To consider something well, of course, is to evaluate both sides of an argument, but unless we also go the extra mile of deliberately forcing ourselves to consider alternatives—not something that comes naturally—we are more prone to recalling evidence consistent with a proposition than inconsistent with it.
Overcoming this mental weakness, known as confirmation bias, is a lifelong struggle; recognizing that we all suffer from it is a important first step.To the extent that we can beware of this limitation in our brains, we can try to work around it, compensating for our in-born tendencies towards self-serving and biased recollections by disciplining ourselves to consider not just the data that might fit with our own beliefs, but also the data that might lead other people to have beliefs that differ from our own.