Strangeness Minus Three

 An old documentary found on the BBC iplayer 'Strangeness Minus Three' has a short tutorial by the great Richard Feynman. Of the many quotes attributed to him is the statement that 'to truly understand something you must be able to teach it',  something he does very well in this 1960's tv show. Its a perfect example that if something is complicated then the problem is not fully understood.