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Lessons from Sherlock Holmes: Don't Decide Before You Decide


When we make a decision, we are, in fact, deciding. It's plain common sense. The definition of a decision. A tautology if ever there was one. Right? Actually, wrong. While it may indeed seem a commonsensical tautology, the truth is that we often decide long before we're making a decision: our preconceptions, biases, behavioral habits and usual ways of acting have long since decided for us.

In “A study in Scarlet,” Holmes coaches Watson on the fallacy of precipitous action. When Inspector Gregson asks for the detective's assistance into a mysterious murder, the duo set out for Lauriston Garden to examine the circumstance of the death. In the hansom, Watson finds himself in depressed spirits and addresses Holmes petulantly:

“You don't seem to give much though to the matter in hand,” I said at last, interrupting Holmes's musical disquisition.

“No data yet,” he answered. “It is a capital mistake to theorize before you have all the evidence. It biases the judgment.”

“You will have your data soon,” I remarked, pointing with my finger; “this is Brixton Road, and that is the house, if I am not very much mistaken.”

“So it is. Stop, driver, stop!” We were sill a hundred yards or so from it, but he insisted upon our alighting, and we finished our journey upon foot.

In this, the first case that Watson witnesses first hand, Sherlock Holmes gets at one of the central elements that set him apart from most everybody else: his constant, habitual discipline of not theorizing before gathering all of the evidence. He is aware of something that most people never realize. Long before we form a judgment, unless we have expressly resisted forming any preconceptions or reasoning out before becoming acquainted with the full intricacies of the situation, we become biased. And to avoid this pre-judgment bias takes skill, mental discipline, and constant reminders.

The prevalence of bias

One of the first things a student learns in an introductory decision making course is the existence of countless biases and heuristics that impact a decision long before it is ever made. Here, I want to focus on one in particular, that bears most directly on Holmes's instructions to Watson: the confirmation bias.

The confirmation bias describes one of the most prevalent mistakes made by novice and experienced minds alike--in fact, it is perhaps over-represented among the ranks of so-called senior deciders--and is often considered the single biggest inferential error of reasoning. It entails gathering evidence to support a viewpoint that has already been established in your mind and interpreting any available evidence in a way that supports that viewpoint.

If, for instance, Holmes were to follow Watson's advice--instead of Watson following Holmes's--and give substantial thought to the Lauriston Garden mystery before he even arrives on the scene, he may well develop a view in his mind of how events unfolded. He would then proceed to see those things that confirmed his view and either discard or fail to notice altogether any evidence to the contrary. And any ambiguous clues that could go either way would be seen as unambiguously contributing to his already formed theory. The result? With each piece of “evidence” he would feel more and more assured that his original idea was the correct one. Else how could everything be falling so neatly into place?

But what about all of the pieces he didn't see because he was not looking for them? All of the pieces he twisted to fit his viewpoint instead of taking them as they were? All of the data that could have told another story but that was never given a chance to speak? None of that would even be noticed, let alone taken into account.

And that is precisely why Holmes is Holmes: he will not theorize before the evidence is in hand. He understands the necessity of gathering it in as open-minded and unbiased a way as possible. That quality is a rare one indeed. From early childhood, we seem to be susceptible to forming confirmatory biases, to deciding long before we actually decide.

In one early study of the phenomenon, children as young as third grade were asked to identify which features of sports balls were important to the quality of a person's serve. Once they made up their mind (for instance, size matters but color does not), they either altogether failed to acknowledge evidence that was contrary to their preferred theory (such as the actual importance of color - or the lack thereof of size) or considered it in a highly selective and distorting fashion that explained away anything that didn't correspond to their initial thought. Furthermore, they failed to generate alternative theories unless prompted to do so, and when they later recalled both the theory and the evidence, they misremembered the process so that the evidence became much more consistent with the theory than it had been in reality. In other words, they recast the past to better suit their own view of the world.

And as we age, it only gets worse--or at the very least, doesn't get any better. Adults are more likely to judge one-sided arguments as superior to those that present both sides of a case--and more likely to think that such arguments represent good thinking (just think of politicians and political debates; they seem to have gotten than notion down). We are also more likely to search for confirming, positive evidence for hypotheses and established beliefs even when we are not actually invested in those hypotheses: in a seminal 1956 study, researchers found that study participants tested a concept by only looking at examples that would hold if that concept were correct - and failed to find things that would show it to be an incorrect one. Finally, we exhibit a remarkable asymmetry in how we weigh evidence of a hypothesis: we tend to overweight any positive confirming evidence and underweight any negative disconfirming evidence--a tendency that professional mind readers have exploited for ages. All of these findings have since been replicated multiple times, in multiple contexts, among multiple age groups. And they stand strong. We see what we are looking for.

Unless we work actively to counteract it, the tendency toward an acting confirmatory bias remains a strong one throughout life, reinforced by a bias toward action and away from thought, toward quick decisions and away from careful reflection. Holmes has worked diligently at his ability to wait for evidence before he puts his formidable brain to use; in the meantime, he will discourse on music. And Watson--Watson comes to Holmes unspoiled. He is the quintessential study subject in one of the psych experiments cited above, eager to get going and to seek out evidence that will support some earlier judgment.

But remember: this is only their first case together. With time, Watson will learn not to interrupt Holmes's thought process, to appreciate the detective's need for space and reflection, his reluctance to speak ahead of time or act rashly under any circumstances. And while he may still be tempted to act first and think later, he will at least recognize the general concept: think first, act later, and try your utmost to approach every decision with a fresh mind. Otherwise, you may find that you have long since decided by the time you actually decide.

Photo credit: “A Study in Scarlet.” By D. H. Friston (, study-01df) [Public domain], via Wikimedia Commons

Previously in this series:

Don’t Just See, Observe: What Sherlock Holmes Can Teach Us About Mindful Decisions

Lessons from Sherlock Holmes: Paying Attention to What Isn’t There

Lessons from Sherlock Holmes: Cultivate What You Know to Optimize How You Decide

Lessons from Sherlock Holmes: Perspective Is Everything, Details Alone Are Nothing

Lessons from Sherlock Holmes: Don’t Underestimate the Importance of Imagination

Lessons from Sherlock Holmes: Confidence Is good; Overconfidence, Not So Much

Lessons from Sherlock Holmes: The Situation Is in the Mindset of the Observer

Lessons from Sherlock Holmes: The Power of Public Opinion

Lessons from Sherlock Holmes: Don’t Tangle Two Lines of Thought

Lessons from Sherlock Holmes: Breadth of Knowledge Is Essential

The views expressed are those of the author and are not necessarily those of Scientific American.

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