Design for the Ordinary

Recently, there have been lots of talk about anomalies, extraordinary situations, “Black Swan” events, and high-volatility in stock market prices. You likely know what I’m talking about…

Designing for the extraordinary is something that occupies a large portion of the mental effort, prototype iteration count, physical testing, and overall evolution of the design concept throughout the various stages of design. We are interested in that one critical condition, that 100-year flood, that 1 millionth cycle, or that worst-case loading condition when the aircraft is full of passengers and luggage, the fuel tank is full, one engine is malfunctioning, and there is a tailwind during take-off. Not a good situation to find ourselves in, but a situation, nonetheless, that still needs to be evaluated.

We generally design for these extreme conditions and use them as targets, goals, objectives, and performance measures, that are simply non-negotiable and must be achieved if our design is to ever be considered acceptable.

But what about the ordinary conditions? Do we ever design to those? Do the ordinary conditions get subsumed by the extraordinary ones? Should we ever focus on the normal, the usual, the typical?

The answer to that last question is yes, but we should be aware of when adding a requirement for the normal or average condition makes sense, and when it does not.

Perhaps painting a vivid picture for your mind’s eye might be the best way to describe this phenomenon.

Robert Wadlow was almost 9 feet tall. He was definitely an extreme case and the Guinness Book of World Record holder as the tallest person ever recorded. Now, what if by law everything in our society had to be designed for people who were 9 feet tall? After all, people who are almost 9 feet tall do or have existed in our society. Discrimination against tall people could be illegal someday.

First of all, every room in almost every building would have to be taller so that Wadlow could stand straight up. Buildings might be the same overall height but there would be a fewer number of floors, with less total square footage. Elevators would need adjusting, normal doors would need to be extended, and escalators would require larger above-head clearances. Our cars would be bigger, and taller, and longer.  They would weigh more and likely have a lower fuel efficiency as a result. Buses would need to be bigger and taller as well. Same things for trains and bikes. Airplanes? Airplanes would look very different, from the cockpit size and seats to the shape and dimensions of the restrooms to the height of the cabins. This doesn’t even begin to touch the passenger seat dimensions which would have to be completely revamped.

Our homes and apartments would have to be scaled up accordingly too. Every room might now have vaulted ceilings, huge doors, tall mirrors, larger hallways, and longer beds. Showers, tubs, garage doors - everything is bigger, longer, or taller. Amusement park rides and rollercoasters would need to be redesigned.  Desks and chairs need to be redesigned. Picnic tables, fitness machines, sports stadiums? Yes, they all would have to be redesigned.

I could go on, but hopefully, you see the picture.

So, why don’t we design for the extreme conditions in user height for the vast majority of products in the world? Simple: cost, time, energy, weight, and a host of other design attributes are valued even more than satisfying those that would accommodate extreme human height.

In essence, we have collectively decided that designing to a reasonable level somewhere below the extreme condition is an acceptable compromise. We have traded the comfort for a small portion of the world’s population so that everything else can be affordable and functional for the majority. Design Tyranny of the Majority? Yes, maybe. But we wouldn’t have as many products and technological advancements if everything was twice as big and 10 times more expensive. So maybe it makes sense.

This is why if you are short or tall, you will inevitably run into some design that doesn’t work for you because of your size. In fact, almost everyone has at least one attribute where they fall into the outlier portion of the distribution.  Your eyes aren’t perfect? That sign’s font is too small. You’re colorblind? Those traffic lights are red and green.  Slow reader? The marquee sign is rolling too fast. A little overweight? Those airplane armrests can’t be lower. Big fingers? Can’t text on small phones. The list goes on and on but likely there is something you personally have been annoyed with because of your natural attributes.

Furthermore, these attributes even change throughout our lives. Most children I know are shorter than me and many senior citizens over 80 can’t see as well as me. This means riding a bike, driving a car, or picking up a watermelon at the store can be difficult for them. It was for me when I was a kid, and I’ll probably return to that state as a very old man. But for now, a lot of products and processes are adequately designed for me physically because I’m squarely in the bulge of the normal distribution across many of the attributes.

A US Supreme Court Justice, Oliver Wendell Holmes, is known for expressing that “Hard cases make bad law [1]” suggesting that if we let outlier cases drive the laws we embraced we may be doing a disservice to ourselves in the future. This might be why the Tax Code is so long and incomprehensible to almost everyone who isn’t a computer. The exceptions and outlier performances (like sporting events) are interesting and fun to explore, discuss, and share, and we can even learn from these unusual events, but we can’t or shouldn’t always make decisions on these rare occurrences. They may be too costly in some way.

This designing for the ordinary is often described as “percentile designing.” For example, a standard airplane seat belt needs to accommodate all passengers up to the 95th percentile in weight and size. If someone is above that, they may need a seat belt extender. Other products with percentile designing might be two-sided, with a percentile on the bottom side too.  For example, a car’s brake and gas pedals must be reachable by an adult between the 5th and 95th percentile of a full-grown human. Taller and shorter people outside of that range will need to purchase a different car or will require modifications.

Other products will have requirements for designing to the ordinary, which don’t include human attributes. Anything with a distribution can potentially fall within this category: air temperatures, tidal heights, precipitation levels, the composition of the dirt, wind speeds, earthquake strength, tornado frequency, etc. are just some of the environmental attributes that engineers and designers must consider. They must decide if designing for the extreme or extraordinary is even possible, or if designing for the ordinary, using design percentiles or something similar, makes more sense with respect to the budget, time, and other internal and external constraints.

As you approach a design challenge and need something to last 10000 cycles, keep stresses under 30 psi, and hold more than 1000 pounds, don’t forget while defining your requirements to ask yourself if designing for the ordinary is also an essential element in keeping your costs, size, and weight to acceptable, reasonable, or optimal levels.

[1] The author recognizes Eric Greitens’ book, “Resilience,” for bringing this quote to the author’s attention.