Cheating isn’t a problem that you’d think an engineer would be tasked with solving. But it was in one notorious case.

On a beautiful April day in 1980, a woman named Rosie Ruiz ran the Boston Marathon in record time. Her time of 2 hours, 31 minutes was surprising, especially because she’d only run one marathon before, nearly half an hour slower.

Kathrine Switzer, the first woman to run the Boston Marathon, interviewed Ruiz on TV after the race, and asked her how she was able to improve so quickly. Ruiz didn't seem to know.

Switzer asked Ruiz if she’d been doing heavy intervals, workouts designed to improve speed. Again, Ruiz was stumped.

She didn’t sound like someone who’d just set a new race record. And she didn’t look like she’d even broken a sweat. People were immediately skeptical.

Guru Madhavan is an engineer who tells Rosie Ruiz’s story in his new book, Applied Minds: How Engineers Think. “This is the Boston Marathon,” he says, "You have people everywhere. You have video cameras. And then you have thousands of reporters everywhere. And no one saw her actually running the course.”

But people did see her entering the course about a half mile from the finish. Ruiz was eventually stripped of her medal – but there was a bigger issue at stake.

“That raised a huge design conundrum for marathon organizers,” Madhavan says. “How do you prevent misconduct going forward? How do you catch cheaters?”

To answer that question, marathon organizers in New York turned to David Collins. He had designed a system of tracking trains he called KarTrak. It used what was then a pretty unusual technology: the bar code.

Collins worked out a system that would allow runners to be scanned and have their times accurately recorded.

Madhavan says that this kind of flexibility with new ideas and technologies is key to being a good engineer. And he insists that all of us should start thinking, at least some of the time, like engineers.

“There are only two systems the way I see it,” Madhavan says. “Systems of nature and systems of engineering. How did we, as ingenious humans... build the world we live in?”

Madhavan breaks the engineering mindset into three parts:

1. Find Structure

“Engineering is about creating,” Madhavan says. And to do that engineers must bring structure to a problem that has none.

Anyone can imagine a bridge where there isn’t one, he argues. “What a good engineer does is imagine the forces and the stresses and the strains on the load-bearing columns of the bridge that don’t even exist. Now that’s the beauty.”

Those forces provide a structure, which brings us to the second principle that guides the engineer's mind

2. Work With The Constraints

“Constraints are everywhere in life and they come in all different directions,” Madhavan says.

Two of the biggest are time and money.

“If you’re building an airplane, you’re limited by budget, you’re limited by the time,” Madhavan says. “And the physical laws of nature often dictate engineering design.”

As you figure out what your constraints are, you winnow away the possible answers to a problem.

3. Make Trade-Offs

You’ve got to decide how best to work with those constraints. That means making some trade-offs.

“This is something we do in life, too,” Madhavan says. “But in a design process, it’s completely different.”

It’s all about “considered judgments, balancing priorities, removing weaker goals against stronger goals,” he adds.