"Excellence is an art won by training and habituation: we do not act rightly because we have virtue or excellence, but we rather have these because we have acted rightly; 'these virtues are formed in man by his doing the actions'; we are what we repeatedly do. Excellence, then, is not an act but a habit: 'the good of man is a working of the soul in the way of excellence in a complete life... for as it is not one swallow or one fine day that makes a spring, so it is not one day or a short time that makes a man blessed and happy."
(1885-1981) American psychologist, philosopher
The Story of Philosophy: The Lives and Opinions of the World's Greatest Philosophers (1926), Ch. II: Aristotle and Greek Science; part VII: Ethics and the Nature of Happiness
Often misattributed to Aristotle by taking Durant's summation of Aristotle's ideas as being the words of Aristotle himself.