The Swiss Cheese Model

A business owner in Chattanooga, Tenn., dropped his children off at school one morning in May 2007, then drove to his office, arriving at about 8:30 a.m. Awhile later, his car’s motion-detector alarm went off. He looked out his office window to the parking lot, but couldn’t see anyone near his car, so he remotely shut off the alarm and went back to work. He did the same thing when the alarm went off a second and then a third time. Shortly after 3 p.m., when he returned to the car to run an errand, he discovered the body of his 15-month-old son in the car seat. Cause of death: hyperthermia. Fire officials reported the temperature inside the car had reached 142°F.

How could a parent forget a child was in the car for even a couple of hours, let alone all day? What’s at the root of this incomprehensible behavior, and what can we learn from it? These are questions Washington Post staff writer Gene Weingarten explored in interviews with 13 people who have experienced this tragedy. What he discovered, as described in his 2009 article, “Fatal Distraction,” is that it’s never intentional, it happens to people from all walks of life, and it typically occurs when “an otherwise loving and attentive parent one day gets busy, or distracted, or upset, or confused by a change in his or her daily routine, and just ... forgets a child is in the car.” 

Holes in the System

In discussing how errors like this happen, Weingarten points to a theory called the Swiss cheese model, which was first described in 1990 by the English psychologist James Reason. As the name suggests, it uses an analogy to imagine the systems humans design to prevent errors as a layered stack of Swiss cheese slices. An error that gets through a hole in the first “slice” or layer is stopped by the second layer, and so on, such that a single-point failure does not lead to total failure of the system. When on rare occasions an error gets all the way through, it’s usually due to a series of seemingly random conditions that cause the holes in successive layers of protection to line up.

A change in your business stresses people and systems, whether it’s caused by an unfamiliar type of work, a project that is significantly larger than average, or one that puts you under unusual time pressure to complete.  

In 2013, such a series of random conditions led to another seemingly impossible error at a California hospital in which a nurse gave a patient 38 times the intended dose of an antibiotic, an incident explored in a series of articles in Wired magazine excerpted from The Digital Doctor, a book by Robert Wachter, MD. In this case, the dosage had been entered by an experienced physician, double-checked by the hospital pharmacist, filled by a state-of-the-art robot, and checked again by the nurse using a bar code reader just before she administered it. Prominent among the contributing causes were an overreliance on technology, a false assumption by the prescribing doctor that led her to ignore a software alarm, a distracted pharmacist, and a nurse working in an unfamiliar ward who ignored her instincts because she didn’t want to interrupt her overworked colleagues.

Mistakes Don’t Happen, They’re Made

Fortunately, remodelers don’t often find themselves in these kinds of life-and-death situations, but when I think about the kinds of mistakes business owners commonly make, those random conditions—being busy, distracted, or upset—come easily to mind. But the effect of a change in routine is, I think, particularly underappreciated as a root cause of mistakes.

For example, when you take on work outside your company’s normal territory, it creates a series of strains on your systems. Employees who must commute farther may experience fatigue and emotional stress, which can affect both physical performance and decision-making. Even with smartphone technology, working at distance complicates your ability to manage a project, especially if it means dealing with unfamiliar suppliers and subtrades.

A change in your business stresses people and systems, whether it’s caused by an unfamiliar type of work, a project that is significantly larger than average, or one that puts you under unusual time pressure to complete.  

We learn from our mistakes, or so the saying goes, and what we learn is to not make the same mistake twice. But I think it’s more important to learn from the mistakes of others, because that helps us to avoid making a mistake in the first place.