  What is really going on here is that we are appealing to principles to rectify a natural distortion in moral judgement. If such judgement focuses only on the reasons present in the case before us, it is all too easy to twist those reasons to suit oneself. So we use principles to stop ourselves from doing that. But really the remedy for poor moral judgement is not a different style of moral judgement, principle-based judgement, but just better moral judgement. There is only one real way to stop oneself distorting things in one’s own favour, and that is to look again, as hard as one can, at the reasons present in the case, and see if really one is so different from others that what would be required of them is not required of oneself. This method is not infallible, I know; but then neither was the appeal to principle.