By this time her old disposition had begun to rouse again. She had been doing her duty, and had in consequence begun again to think herself Somebody. However strange it may well seem, to do one’s duty will make any one conceited who only does it sometimes. Those who do it always would as soon think of being conceited of eating their dinner as of doing their duty. What honest boy would pride himself on not picking pockets? A thief who was trying to reform would. To be conceited of doing one’s duty is then a sign of how little one does it, and how little one sees what a contemptible thing it is not to do it. Could any but a low creature be conceited of not being contemptible? Until our duty becomes to us common as breathing, we are poor creatures.
--from "The Wise Woman" by George MacDonald