There is a difference between doing some particular just or temperate action and being a just or temperate man. Someone who is not a good tennis player may now and then make a good shot. What you mean by a good player is the man whose eye and muscles and nerves have been so trained by making innumerable good shots that they can now be relied on. They have a certain tone or quality which is there even when he is not playing, just as a mathematician's mind has a certain habit and outlook which is there even when he is not doing mathematics. In the same way a man who perseveres in doing just actions gets in the end a certain quality of character. Now it is that quality rather than the particular actions which we mean when we talk of "virtue."
C.S. Lewis, Mere Christianity, p. 77