I came across this quotation early on in my teaching career, and it has stayed with me.
Today, (thank you google and Wikipedia), I discovered that it is a quotation from a Frenchman, Joseph Joubert, a moralist and essayist, born in 1754. He didn’t publish anything during his own lifetime, but Chateaubriand (I always thought that was a kind of steak; thank you Wikipedia, again,) collected and published his work posthumously. I’m glad he did; this quotation has been so influential in my own teaching approach.