“There are two different occasions upon which we examine our own conduct, and endeavour to view it in the light in which the impartial spectator would view it: first, when we are about to act; and secondly, after we have acted. Our views are apt to be very partial in both cases; but they are apt to be most partial when it is of most importance that they should be otherwise. When we are about to act, the eagerness of passion will seldom allow us to consider what we are doing, with the candour of an indifferent person. . . . When the action is over, indeed, and the passions which prompted it have subsided, we can enter more coolly into the sentiments of the indifferent spectator.”