Cracking up about patterns and cause

I just received an email from a contractor in Austria who described a legal problem that many contractors face. Apparently, demolition crews are sued regularly by homeowners for damage to nearby homes. After a blast that causes vibration in a house, homeowners search their house and discover big cracks. They then blame the cracks on the nearby blasts and the vibrations they cause. According to the contractor, these newly discovered cracks likely were there all along; most houses develop cracks as they age and settle. The key is that people didn’t notice the cracks until they started looking for them.

In some ways, this phenomenon is the opposite of change blindness (the failure to notice large changes that we discuss in Chapter 2 of the book)—in essence, people are blind to the lack of change. They see change where none actually existed because they assume they would have noticed a big crack had it been there all along. If the crack is distinctive after they know to look for it, they assume that they would have noticed it even if they weren’t looking for it. But the cracks don’t draw attention automatically, and you won’t spot them until you search for them. Once you do look for cracks, you likely will see them everywhere. The same principle explains why, after being dumped by your girlfriend or boyfriend, every song on the radio is about relationships. It’s unlikely that radio stations are attuned to your romantic status—they were playing a similar rotation of songs before and after your breakup, but you’re now focusing attention on relationships, so you notice.

The problem is that we intuitively believe that distinctive objects, events, and features—like a crack in the wall—automatically draw attention, when in reality, it takes effort to find them. Once we know about them, they’re obvious. Before we know about them, they’re invisible. Our intuitions about how attention and the mind work lead us to the wrong conclusion: I couldn’t have missed something so obvious, so it must be new. In the case of vibration, homeowners mistakenly attribute the newly detected cracks to the most obvious, recent, external event (vibration from a blast). Mistaken intuitions about attention and perception prevent the homeowners from spotting the real reason they hadn’t noticed cracks before: we often don’t see what we’re not looking for.

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