I have always been fond of the West African proverb “Speak softly and carry a big stick; you will go far.”

Theodore Roosevelt (1858-1919) US President (1901-1909)
Letter to Henry L. Sprague (26 Jan 1900)

Full text. This is the first known use by Roosevelt of his future catch phrase.  It attained more fame when he used it in a speech at the Minnesota State Fair (2 Sep 1901) (there are transcript variants):

• "There is a homely adage which runs 'Speak softly and carry a big stick; you will go far.' If the American nation will speak softly and yet build and keep at a pitch of highest training a thoroughly efficient Navy, the Monroe Doctrine will go far."
• "Right here let me make as vigorous a plea as I know how in favor of saying nothing that we do not mean, and of acting without hesitation up to whatever we say. A good many of you are probably acquainted with the old proverb, 'Speak softly and carry a big stick — you will go far.' If a man continually blusters, if he lacks civility, a big stick will not save him from trouble, and neither will speaking softly avail, if back of the softness there does not lie strength, power. In private life there are few beings more obnoxious than the man who is always loudly boasting, and if the boaster is not prepared to back up his words, his position becomes absolutely contemptible. So it is with the nation. It is both foolish and undignified to indulge in undue self-glorification, and, above all, in loose-tongued denunciation of other peoples. Whenever on any point we come in contact with a foreign power, I hope that we shall always strive to speak courteously and respectfully of that foreign power."