A strong and wise people will study its own failures no less than its triumphs, for there is wisdom to be learned from the study of both, of the mistake as well as of the success.
 Theodore Roosevelt, State of the Union Address. copy citation

Context

“The chance for the settlement of disputes peacefully, by arbitration, now depends mainly upon the possession by the nations that mean to do right of sufficient armed strength to make their purpose effective. The United States Navy is the surest guarantor of peace which this country possesses. It is earnestly to be wisht that we would profit by the teachings of history in this matter. A strong and wise people will study its own failures no less than its triumphs, for there is wisdom to be learned from the study of both, of the mistake as well as of the success. For this purpose nothing could be more instructive than a rational study of the war of 1812, as it is told, for instance, by Captain Mahan. There was only one way in which that war could have been avoided.” source