Who dares to teach must never cease to learn.

John Cotton Dana (1856-1929) American librarian
Building Inscription, Newark State Teachers College

Dana was asked to supply a Latin quotation to be inscribed on a new building at Newark State Teachers College (now Kean University). Unable to find an appropriate Latin phrase, he authored this English one instead, which eventually became the college motto (see The New York Times Book Review, 5 Mar 1967).   The university motto has since been shortened to Semper Discens ("Always Learning"). 

Sometimes attributed to Richard Henry Dann.