Richard Feynman was an American physicist who is best known for his work on QED (quantum electrodynamics, and a pun on the Latin phrase ‘quod erat demonstrandum’). He also developed the now-standard Feynman diagrams and won the Nobel Prize in Physics in 1965.
Feynman was a strong advocate for simplicity and explaining things so that the average person could understand them. He believed that anyone who understood something should be able to explain it to a layperson.
In fact, he believed this so vehemently that once, when he was asked to explain why spin one-half particles obey Fermi Dirac statistics, Feynman initially said that he would prepare a freshman lecture on the subject.
Later he admitted “You know, I couldn’t do it. I couldn’t reduce it to the freshman level. That means we really don’t understand it.” It’s also believed that Feynman said “If you can’t explain it to a six year old, you don’t really understand it.”