Our Most Common Cognitive Error?

Decision Hygiene #3: Substitution

In my last Decision Hygiene post, I introduced the two cognitive systems Daniel Kahneman describes in Thinking, Fast and Slow. System One is excellent at providing mostly-accurate answers quickly when you know a subject very well. System Two is good at avoiding small mistakes and arriving at precise answers through methodical steps.

In this post, I’m going to dive into one of the most common cognitive errors: substitution. It’s not that one system is good or bad – it’s that you use one system when you should use the other. 

The classic bat and ball question I mentioned last time often induces this error. When you hear that the ball is 10 cents, the bat is $1 more than the ball, and the total is $1.10, and you’re asked to find the cost of the bat, it’s very tempting to blurt out, “One dollar!” To be safe, you should engage System Two – grab a pencil and paper, write it out, check your work – but you might not initially realize that it’s a tricky question, and in any case, it’s so much easier to just accept the immediate answer that System One provides.

This error is not limited to math questions. Suppose you need heart surgery. As you meet with the surgeon, you ask yourself, “Is this person competent?” This is actually a very difficult question. You might not even be able to answer it. You don’t have any of the relevant statistics from this person’s recent work, and you wouldn’t have the proper context in which to evaluate them anyway. (Is a 95% success rate good?) You also can’t directly observe their work, and even if you could, would you know for sure that their decisions were optimal? Any serious attempt to determine the competence of your surgeon would require a lot of work on the part of your System 2: gathering relevant statistics, interviewing other experts, analyzing all of the information, etc.

So you don’t answer your own question directly. Instead, you answer a much easier question: “Does this person speak with confidence and authority?” An answer will most likely spring to mind immediately. And it could very well be wrong! One surgeon could speak confidently and make terrible mistakes; another could mumble hesitantly and fail to make eye contact while nevertheless performing brilliantly in the operating room.

Here’s another example. Suppose you are asked, “Are you satisfied with your life as a whole?” This would again require a lot of System Two work. You’d have to evaluate your relationships, your career development, your goals over time, the personal difficulties you’ve endured, and many other factors. But here’s a much easier question: “What is my mood right now?” You can answer that one right away.

Students will often make this same sort of error, replacing a nuanced, demanding question with a much easier one. Consider this question from an old ACT (the paragraph to which it refers is on the left):

This paragraph is pretty odd. The author seems to be saying that the city itself somehow knew that he was about to be born, and it responded by building a lot of stuff. Many students do not understand the paragraph, nor do they even realize that they have not understood it. For these students, the question is quite difficult. They’ll need to go back, re-read the paragraph very carefully, update their initial understanding, and then discriminate between the answers methodically. 

But suppose they substitute a much easier question…maybe, “Do I remember this phrase from the passage?” or “Does this sound logical?”

Answer choice D is immediately compelling. It *was* mentioned in the passage and it *does* sound logical. It ‘clicks’ right away. So students pick this answer over the seemingly-bizarre choice C.

Next post, we’ll look at a specific type of substitution error: our responses to the Halo Effect.