This essay is excerpted from Mastermind: How to Think Like Sherlock Holmes, published this week by Viking.
How do we make sure we don’t fall victim to overly confident thinking, thinking that forgets to challenge itself on a regular basis? No method is foolproof. In fact, thinking it foolproof is the very thing that might trip us up.
Because our habits have become invisible to us, because we are no longer learning actively and it doesn’t seem nearly as hard to think well as it once did, we tend to forget how difficult the process once was. We take for granted the very thing we should value. We think we’ve got it all under control, that our habits are still mindful, our brains still active, our minds still constantly learning and challenged—especially since we’ve worked so hard to get there—but we have instead replaced one, albeit far better, set of habits with another. In doing so we run the risk of falling prey to those two great slayers of success: complacency and overconfidence.
These are powerful enemies indeed. Even to someone like Sherlock Holmes. Consider for a moment “The Yellow Face,” one of the rare cases where Holmes’s theories turn out to be completely wrong. In the story, a man named Grant Munro approaches Holmes to uncover the cause of his wife’s bizarre behavior. A cottage on the Munros’ property has recently acquired new tenants, and strange ones at that. Mr. Munro glimpses one of its occupants and remarks that “there was something unnatural and inhuman about the face.” The very sight of it chills him.
But even more surprising than the mystery tenants is his wife’s response to their arrival. She leaves the house in the middle of the night, lying about her departure, and then visits the cottage the next day, extracting a promise from her husband that he will not try to pursue her inside. When she goes a third time, Munro follows, only to find the place deserted. But in the same room where he earlier saw the chilling face, he finds a photograph of his wife.