The politician has not to revenge what has happened but to ensure that it does not happen again.
Source, in full
In 1867, following public criticism of courtesy shown to the defeated Napoleon III after the battle of Sedan, as quoted in A. J. P. Taylor, Bismarck: The Man and the Statesman (1955), p. 115. Also quoted in Oxford Dictionary of Political Quotations (1997), p. 46.