The valuable advice that C.S. Lewis gave on writing is much repeated, but here is a passage that I’ve rarely seen quoted. It is taken from his book on Milton’s Paradise Lost, and explains the difficulty authors have in portraying virtuous characters.
“It remains, of course, true that Satan is the best drawn of Milton’s characters. The reason is not hard to find. Of the major characters whom Milton attempted he is incomparably the easiest to draw. Set a hundred poets to tell the same story and in ninety of the resulting poems Satan will be the best character. In all but a few writers the ‘good’ characters are the least successful, and every one who has ever tried to make even the humblest story ought to know why. To make a character worse than oneself it is only necessary to release imaginatively from control some of the bad passions which, in real life, are always straining at the leash; the Satan, the Iago, the Becky Sharp, within each of us, is always there and only too ready, the moment the leash is slipped, to come out and have in our books that holiday we try to deny them in our lives. But if you try to draw a character better than yourself, all you can do is to take the best moments you have had and to imagine them prolonged and more consistently embodied in action. But the real high virtues which we do not possess at all, we cannot depict except in a purely external fashion. We do not really know what it feels like to be a man much better than ourselves. His whole inner landscape is one we have never seen, and when we guess it we blunder. It is in their ‘good’ characters that novelists make, unawares, the most shocking self-revelations. Heaven understands Hell and Hell does not understand Heaven, and all of us, in our measure, share the Satanic, or at least the Napoleonic, blindness. To project ourselves into a wicked character, we have only to stop doing something, and something that we are already tired of doing; to project ourselves into a good one we have to do what we cannot and become what we are not.”