In 2012, the creator of the xkcd cartoon Randall Munroe unveiled Up Goer Five — a detailed diagram of the Saturn V rocket, annotated using only the most common 1,000 (sorry, “ten hundred”) words in the dictionary.

It was a viral hit, as was the follow-up book, Thing Explainer (2015), and it produced an intriguing reaction from the science-communication community, who are among the most enthusiastic of Munroe’s many fans. First, there was a burst of people trying to explain their own fields using the same constraint. Then came the backlash.

“Condescending”, wrote one science blogger. “By talking down to our audience, we risk alienating them, and reinforcing the common preconception that scientists consider and hold themselves apart from non-scientists.” The great science writer Carl Zimmer criticised the craze (not the cartoon) for encouraging the idea that there was anything useful in the constraint. The craze was, he argued, a disheartening waste of time for any scientist trying to figure out how to explain their field to a lay audience, because they might wrongly conclude that it was hopeless to try.

Well, maybe. Up Goer Five is tremendous fun but more puzzling than pellucid. The typical three-year-old can recognise 1,000 words, and there is nothing particularly clarifying about trying to explain something complicated while limiting oneself to the vocabulary of a three-year-old.

Nevertheless, unreasonable-seeming constraints can produce surprisingly powerful results. The artist and writer Theodor Geisel was once given the challenge of writing a book for six-year-olds while deploying no more than 225 different words from a short list. At first, Geisel was frustrated at the lack of adjectives; it was “like trying to make a strudel without any strudels”. But then, as David Epstein explains in his book Inside the Box: How Constraints Make Us Better (2026), he grabbed the first two rhyming words and went for it. The result, The Cat in the Hat (1957), made Geisel — better known as Dr Seuss — a phenomenon. Green Eggs and Ham (1960) is even better, and while it is packed with crazy situations, it contains only 50 unique words, making Up Goer Five seem positively lexiphanic. (Dr Seuss took on that challenge to win a bet.)

In the arts, the value of constraints is not a new idea. Monet almost never used black paint. Bach tied himself in knots with self-imposed rules, and part of the joy of his music comes from hearing him untie and retie them with ease. Miles Davis recorded Kind of Blue (1959) with no rehearsal, minimal composition and used the first take of each piece.

But when it comes to a more practical problem, is it really tenable to impose needless constraints? Perhaps it is. The simplest constraint for anyone trying to explain a complex topic is to accept the request to “explain it to me like I’m 10 years old”. What’s packed into that request is, vividly exaggerated, the reminder that what seems obvious to an expert is often incomprehensible to the listener. Technical jargon and fusillades of acronyms are often used to convey an explanation that has been denuded of all the foundations and context that might allow it to make sense.

Worse, in a kind of inverted Dunning-Kruger effect, the very expertise that makes the expert worth consulting also makes it hard for the expert to imagine what it was like to know nothing about the topic.

Hence “explain it to me like I’m 10 years old”. If you are reading this column you definitely aren’t a typical 10-year-old, but the image of the bewildered 10-year-old gives the expert an anchor to help them slow down and simplify. My book, The Truth Detective, was supposed to be a version of How to Make the World Add Up for 10-year-olds. My wife tells me she prefers it to the one that was for the grown-ups.

What is true in technical communication may also be true in design. David Epstein describes the moment the US Army tried to adapt its body armour for female soldiers. As Caroline Criado Perez forcefully argues in Invisible Women, women are not merely scaled-down men and are not well served by equipment designed for men. But as the US Army started grappling with that challenge, they discovered some surprising benefits. They were able to replace 11 sizes of body armour with just eight sizes by making the armour a modular mix-and-match system. This simplified manufacture and logistics while greatly expanding the options available to an individual soldier.

Meanwhile, many of the men in the army found the “female” modules a better fit — a narrow vest gave room to soldier a rifle, while a notch in the back of the helmet designed to accommodate hair buns allowed all soldiers, regardless of hair-do, to raise their heads while prone. “A new, more meticulous sizing process that benefitted women benefitted everyone,” Epstein writes.

A similar story can be told about designing for people without a full range of mobility or senses. In 1972, design professor Marc Harrison and his students produced a demonstration house full of features that accommodated users with special needs — flat thresholds between rooms made life easy for wheelchair users and people on walking frames; levers on taps and door handles are easier to use for people with a weak grip. But, of course, levers are easier for anyone to use — try twisting an old-fashioned doorknob with a cup of coffee in each hand.

Subtitles help people who can’t hear what the actors are saying — and it turns out that, for some gritty dramas, that is all of us. Web pages that are designed with screen readers for the blind in mind are typically better structured, simpler and friendlier for mobile devices. The Oxo kitchen appliance company was founded by a retired cookware entrepreneur whose wife had arthritis, but the chunky rubber handles are far more widely enjoyed. And of course, the dropped kerb may be life-changing for wheelchair users but it is pretty convenient for anyone pushing a pram.

The challenges faced by users who are unusually small, large, old or young, or who have disabilities, are, writes Epstein, “more extreme versions of the challenges that many other users face”.

Of course, we should not make the mistake of arguing that the reason we should design for disabled people is to help the majority, or that we should design for women because of the benefits for men.

But in a world where it is often hard to put ourselves in the shoes of someone else, the challenge of explaining the world to a 10-year-old, or designing a jar that an octogenarian can open, is sometimes just a prompt to do a better job of what we were trying to do in the first place.

Written for and first published in the Financial Times on 15 July 2026.