If we examine the different shades and gradations of weakness and self-command, as we meet with them in common life, we shall very easily satisfy ourselves that this control of our passive feelings must be acquired, not from the abstruse syllogisms of a quibbling dialectic, but from that great discipline which Nature has established for the acquisition of this and of every other virtue; a regard to the sentiments of the real or supposed spectator of our conduct.
Adam Smith, Theory of Moral Sentiments Part 3, Chapter 3.
"The real or supposed spectator" is an important part of Smith's moral theory; he argues that we improve and refine our moral sense by creating an objective viewpoint - that of the impartial spectator - and seeing our actions in that light as well as in our own more biased perspective. (Impartial spectator theory should not be confused, by the way, with 'ideal spectator theory', which is different altogether. In impartial spectator theory the idea is that the moral perspective is a normal human perspective; in ideal spectator theory, it is that the moral perspective is an unlimited perspective.)