Richard Feynman
If you cannot teach it, you have not got it
Jargon is where the hole hides
His teaching at Caltech, as recorded by David Goodstein
The internet sells this as a study hack in four steps. This page is about the harder claim sitting underneath it.
What actually happened?
David Goodstein once asked him to explain why spin one-half particles obey Fermi-Dirac statistics. Feynman sized up his listener and said he would prepare a freshman lecture on it. He came back a few days later. I couldn't reduce it to the freshman level, he said, and that means we don't really understand it. The sentence everyone quotes about explaining things simply is not in his writing. What is documented is this, and the line found on his blackboard when he died: what I cannot create, I do not understand.
Ban the jargon and the hole shows at once
A technical term is a compression, and compression only works if both sides can unpack it. Forbid the term and you have to unpack it yourself. Wherever you cannot, you were storing a label rather than an understanding.
Explain your job to someone at home. Every point where you fall back on the trade word is a point you have not thought through.
Deriving it once beats memorising it ten times
A remembered conclusion works on the question it came from. A derivation works on the whole class of questions, because on the way through you collide with why it could not have been otherwise. Those collisions are the structure of understanding.
Rather than memorising when the formula applies, work out once where it comes from. After that the conditions are obvious and need no memorising.
Teaching is the test, not the favour
The usual reading is that explaining helps the listener. His use runs the other way: he explained in order to find out whether he knew. Which means the more ignorant the audience, the better the instrument.
A colleague silently repairs the steps you skipped. Somebody outside the field stops dead at the first vague sentence, which is the reading you wanted.
How do I use it today?
Where you are: you think you understand something and are not certain.
Ask first: without one term of art, can you take an outsider to the point of nodding? Which sentences do you stall on?
Where it goes wrong: confusing simple with shallow — what gets simplified is the telling, never the content.
Lines to keep
That means we don't really understand it.
What I cannot create, I do not understand.
Same situation, other people are asking
I read a lot and can't recall any of it when it matters.I've done the reps and it still isn't automatic.What I learned only works in the shape I learned it.I take in everything and keep nothing. What should I be leaving out?Nothing I study stays · all 8 questions →If this one named what you are going through,
send it to someone who needs it, or keep it somewhere you will find it again.