Learning & thinking · a life skill
Simple Feynman Explanations
explain it to a twelve-year-old, on one page
You don't know how well you understand something until you try to say it simply. Write the idea down for a twelve-year-old, and the words you can't explain show up on the page: those are what to read next.
- Easy to start
- Medium impact
- Learn it in 1 week
- One page, ten minutes
The crossed-out words are the gaps. A number usually closes them faster than a definition.
Tonight, ten minutes
Try it now.
A pen, one blank page, and an idea you think you know. Hover a step to find it on the page.
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Pick one idea
Write its name at the top of a blank page. One idea, not a subject: “compound interest”, not “investing”.
the heading -
Explain it to a twelve-year-old
In full sentences, the way you'd say it out loud, with your notes closed.
the first try -
Cross out what they'd ask about
Every word they couldn't explain back, and every “basically”. Each one is a gap you skated over.
the crossings-out -
Look up only those, and write it again
Put a real number or an example in. Most gaps close the moment a number goes in.
again, plainer -
Stop when they could say it back
If you can picture them putting it in their own words, you have it.
the last line
For example: “Inflation is a rise in the general price level” has two words to cross out. Plainer: a sandwich that cost $5 last year costs $5.15 now, so the same $5 buys a little less. That's 3% inflation.
Before you rewrite
Check your page.
Type or paste your first try. The checker marks long words and hand-wave words like “basically”. A mark isn't a mistake. It's a word to ask yourself about: could a twelve-year-old explain it back?
Nothing you type leaves this page or is saved.
- Long words
- –
- Hand-waves
- –
- Longest sentence, in words
- –
- long word three syllables or more
- hand-wave sounds like an answer, isn't one
The idea
Why it works.
In 2002 Leonid Rozenblit and Frank Keil asked people how well they understood everyday things, such as how a zipper works. Then they asked them to write the explanation out, step by step, and rate themselves again. The ratings fell. We feel we understand far more than we can explain, and they named it the illusion of explanatory depth.
Writing for a twelve-year-old breaks that illusion before it costs you. Richard Feynman learned the habit from his father, who told him a bird's name in several languages and then pointed out that none of them said anything about the bird. “I learned very early,” Feynman wrote, “the difference between knowing the name of something and knowing something.” The tidy four-step “Feynman technique” is a later summary of how he worked, not a method he wrote down.
Keep it simple
One page only.
- One page, no more. If it runs over, you've explained two ideas. Split them.
- Notes closed. Write from memory first. The page is a test, not a copy.
- A number beats a definition. “$100 becomes $105” explains more than any sentence about rates.
- Keep the crossed-out words. They're tomorrow's reading list.
Go deeper
Keep going.
- Simple Feynman Explanations
- Deliberate Feynman Explanations
- Advanced Feynman Explanations
Keep this going in the app.
HourLife turns these ideas into a daily system — goals, habits, focus, and reflection in one private place.
