Use the Analogy, Then Throw Away the Ladder

Years ago I explained a web server to a new starter at work as "a waiter who brings you the page you ordered". She nodded, wrote it down, and two weeks later asked me why the waiter kept bringing her an old version of the menu.

That question was better than my analogy. And it taught me more about teaching than anything I'd read.

Why analogies work at all

When you learn something new, your brain doesn't file it in an empty drawer. It hooks the new idea onto something you already know. An analogy gives the brain a ready-made hook. "DNS is a phone book." "Latency is the drive to the shop." Suddenly a word that meant nothing has a shape, a weight and a place to sit.

This is why good analogies feel like relief. The fog lifts. You can explain the thing back to someone else, which is the first real test of understanding. I still use these comparisons every week, in videos and in conversations with people who don't work in tech at all.

But there's a catch that took me a long time to see.

Every analogy is a little bit wrong

A comparison works because two things share some features. It misleads because they don't share all of them. The waiter analogy captured the idea of request and delivery. It said nothing about caching, where copies of a page are kept closer to you so they arrive faster, sometimes long after the original has changed. My new starter had pushed the waiter into territory he'd never been designed for, and he'd fallen over.

The philosopher Ludwig Wittgenstein wrote, near the end of his first book, that his readers should treat his propositions like a ladder: climb up them, then throw the ladder away. He was talking about philosophy, but I think it's the best advice for any analogy. Use it to get up. Then step off it, before you start believing the world is made of ladders.

My neighbour Mr. Mummu learnt this the hard way. He decided to teach his nephew how a car engine works by comparing it to a person: fuel is food, the radiator sweats, the battery is the heart. The nephew loved it. A week later the car wouldn't start, and the nephew, very sincerely, suggested they let it have a nap. Mummu said he'd laughed so hard he forgot to be annoyed. Then he went back and added one sentence to his lesson: "The car is a bit like a person, until it isn't. Here's where it stops." The nephew still calls the radiator "the sweaty bit", but he also knows how to check the coolant.

How I teach with analogies now

I've ended up with a simple habit, and it's made my explanations much more honest.

First, I give the comparison quickly, in one or two sentences, without dressing it up. The goal is a hook. Poetry can wait.

Then I say out loud where it breaks. "DNS is like a phone book, except lots of computers keep their own old copy for a while, which is why changes take time to show up." That second half is where most of the real learning lives. It's also where the learner's next question usually comes from.

Finally, once the person has the idea, I try to switch to the real words and the real mechanism. The analogy has done its job. If we keep leaning on it, we start making decisions based on waiters and phone books instead of servers and records.

The bit I still get wrong

I'm not great at the last step. Analogies are comfortable, and the real explanation is often duller, so I hang on too long. I've caught myself extending a metaphor three sentences past its use-by date because it was getting a laugh.

There's also a fair argument against my approach. Some teachers would say that for beginners, a simple picture is enough, and pointing out the cracks too early just confuses people. Sometimes that's true. If someone only needs to know how to send an email, they don't need a lecture on mail servers.

But whenever someone is going to build something, fix something, or explain it to the next person, I think they deserve to know where the ladder ends.

A small test you can try

Next time someone explains something to you with a comparison, ask one question: "Where does that comparison stop working?"

If they can answer, they understand the thing. If they can't, they understand the analogy.

And if you're the one teaching, try answering that question before anyone asks.