What can be added to the happiness of the man who is in health, who is out of debt, and has a clear conscience? To one in this situation, all accessions of fortune may properly be said to be superfluous; and if he is much elevated upon account of them, it must be the effect of the most frivolous levity. This situation, however, may very well be called the natural and ordinary state of mankind. Notwithstanding the present misery and depravity of the world, so justly lamented, this really is the state of the greater part of men. The greater part of men, therefore, cannot find any great difficulty in elevating themselves to all the joy which any accession to this situation can well excite in their companion.
But though little can be added to this state, much may be taken from it. Though between this condition and the highest pitch of human prosperity, the interval is but a trifle; between it and the lowest depth of misery the distance is immense and prodigious. Adversity, on this account, necessarily depresses the mind of the sufferer much more below its natural state, than prosperity can elevate him above it.
Adam Smith, The Theory of Moral Sentiments, 1759, sect. 1, chap. 3