The Theory of Moral Sentiments by Adam Smith

But though the approbation of his own conscience can scarce, upon some extraordinary occasions, content the weakness of man; though the testimony of the supposed impartial spectator of the great inmate of the breast, cannot always alone support him; yet the influence and authority of this principle is, upon all occasions, very great; and it is only by consulting this judge within, that we can ever see what relates to ourselves in its proper shape and dimensions; or that we can ever make any proper comparison between our own interests and those of other people.

As to the eye of the body, objects appear great or small, not so much according to their real dimensions, as according to the nearness or distance of their situation; so do they likewise to what may be called the natural eye of the mind: and we remedy the defects of both these organs pretty much in the same manner. In my present situation an immense landscape of lawns, and woods, and distant mountains, seems to do no more than cover the little window which I write by, and to be out of all proportion less than the chamber in which I am sitting. I can form a just comparison between those great objects and the little objects around me, in no other way, than by transporting myself, at least in fancy, to a different station, from whence I can survey both at nearly equal distances, and thereby form some judgment of their real proportions. Habit and experience have taught me to do this so easily and so readily, that I am scarce sensible that I do it; and a man must be, in some measure, acquainted with the philosophy of vision, before he can be thoroughly convinced, how little those distant objects would appear to the eye, if the imagination, from a knowledge of their real magnitudes, did not swell and dilate them.