“It is not enough to have a good mind; the main thing is to use it well.”

Yeah, I like this one. As I’ve said before (e.g., here and here), a person’s “practical intelligence” — how well a person can come to the right opinions, make the best decisions, and formulate good solutions to problems in the real world — is determined more by the person’s characteristic habits and attitudes as a critical thinker than by his or her IQ.