Those who can, do, those who cannot, teach.

This and many similar quotes with the same general meaning are misattributed to Aristotle as a result of Twitter attribution decay. The original source of the quote remains anonymous. The oldest reference resides in the works of George Bernard Shaw, Man and Superman (1903): "Maxims for Revolutionists", where he claims that "He who can, does. He who cannot, teaches.".

However, the related quote, "Those who can, do. Those who understand, teach" likely originates from Lee Shulman in his explanation of Aristotlean views on professional mastery | Aristotle, whose works formed the heart of the medieval curriculum, made these observations in Metaphysics (cited in Wheelwright, 1951) | "We regard master-craftsmen as superior not merely because they have a grasp of theory and know the reasons for acting as they do. Broadly speaking, what distinguishes the man who knows from the ignorant man is an ability to teach, and this is why we hold that art and not experience has the character of genuine knowledge (episteme)--namely, that artists can teach and others (i.e., those who have not acquired an art by study but have merely picked up some skill empirically) cannot." . . . | "With Aristotle we declare that the ultimate test of understanding rests on the ability to transform one's knowledge into teaching. Those who can, do. Those who understand, teach."