Thinking tools
The Feynman technique
Test whether you understand something by trying to explain it in plain words to a beginner; where the explanation breaks, your understanding has a gap.
Named after the physicist Richard Feynman, but the four-step method that carries his name (pick a topic, explain it to a child, find the gaps, simplify) is a later popularisation from study and productivity writers; Feynman never wrote it down. What he did do was hold himself to the test, as his Caltech colleague David Goodstein recalled.
Pick an idea and explain it as if to a smart newcomer: no jargon, no skipped steps. Wherever you reach for a technical term, wave your hands or say "it just works that way", mark the spot. Go back to the source, fill the gap, and try again until the explanation runs from start to finish in simple words.
It works because recognition feels like understanding. Rereading notes and nodding along gives you a sense of mastery that collapses the moment you must produce the idea yourself. Jargon also hides gaps: a term can stand in for a step you never understood. Explaining out loud makes each missing step visible.
Simple is not the same as complete. Some ideas lose something real when stripped of their mathematics, and a smooth explanation can still be wrong. The method finds gaps; it does not fill them, and it is no substitute for working problems. Note also that Feynman's own lesson was harsher than the popular version: when he could not simplify something, he concluded that nobody really understood it yet, himself included.
Example
David Goodstein, a Caltech physicist, once asked Feynman to explain why particles with spin one-half obey Fermi-Dirac statistics. Feynman said he would prepare a freshman lecture on it. A few days later he came back: "I couldn't do it. I couldn't reduce it to the freshman level. That means we don't really understand it." Goodstein told the story in Feynman's Lost Lecture, excerpted in Caltech's Engineering & Science magazine in 1996.
Where it applies
Before you approve a design, write the one-paragraph explanation a new team member would need. If you cannot explain why a model's retrieval step helps without saying "embeddings" and stopping, open the code and trace what the step actually does. Writing a clear pull request description is the same test.
Think about it
What part of your daily work could you not explain to a new hire without hiding behind a term you have never unpacked?
Applied it to something real? Log it.
Test yourselfWhat does it mean, under this technique, when you cannot explain an idea in simple terms?
That your understanding has a gap at the point where the explanation breaks. Feynman went further: if he could not simplify it, he took it as a sign that nobody understood it well yet.
Related models
- First principlesBreak a problem down to what you know is true and reason up from there, instead of copying what others have done.
- Circle of competenceKnow where your real understanding ends, and keep your big bets inside that line.
- The map is not the territoryEvery model, metric or plan is a simplification, and the parts it leaves out can matter more than the parts it shows.
- Retrieval practicePulling something out of memory strengthens it more than putting it in again, so a test is a better study tool than a reread.
- ChunkingWorking memory holds only a few items, so experts get around the limit by grouping details into larger units they recognise at a glance.