The wise man must support the propriety of his own conduct in health and in sickness, in success and in disappointment, in the hour of fatigue and drowsy indolence, as well as in that of the most awakened attention. The most sudden and unexpected assaults of difficulty and distress must never surprise him. The injustice of other people must never provoke him to injustice.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“But to support and finish off, if I may say so, the conduct and conversation of a whole life to some resemblance of this ideal perfection, is surely much more difficult than to work up to an equal resemblance any of the productions of any of the ingenious arts. The artist sits down to his work undisturbed, at leisure, in the full possession and recollection of all his skill, experience, and knowledge. The wise man must support the propriety of his own conduct in health and in sickness, in success and in disappointment, in the hour of fatigue and drowsy indolence, as well as in that of the most awakened attention. The most sudden and unexpected assaults of difficulty and distress must never surprise him. The injustice of other people must never provoke him to injustice. The violence of faction must never confound him. All the hardships and hazards of war must never either dishearten or appal him. Of the persons who, in estimating their own merit, in judging of their own character and conduct, direct by far the greater part of their attention to the second standard, to that ordinary degree of excellence which is commonly attained by other people, there are some who really and justly feel themselves very much above it, and who, by every intelligent and impartial spectator, are acknowledged to be so.” source