To man is allotted a much humbler department, but one much more suitable to the weakness of his powers, and to the narrowness of his comprehension; the care of his own happiness, of that of his family, his friends, his country: that he is occupied in contemplating the more sublime, can never be an excuse for his neglecting the more humble department
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“The Meditations of Marcus Antoninus, which turn principally upon this subject, have contributed more, perhaps, to the general admiration of his character, than all the different transactions of his just, merciful, and beneficent reign.14 The administration of the great system of the universe, however, the care of the universal happiness of all rational and sensible beings, is the business of God and not of man. To man is allotted a much humbler department, but one much more suitable to the weakness of his powers, and to the narrowness of his comprehension; the care of his own happiness, of that of his family, his friends, his country: that he is occupied in contemplating the more sublime, can never be an excuse for his neglecting the more humble department; and he must not expose himself to the charge which Avidius Cassius is said to have brought, perhaps unjustly, against Marcus Antoninus; that while he employed himself in philosophical speculations, and contemplated the prosperity of the universe, he neglected that of the Roman empire.15 The most sublime speculation of the contemplative philosopher can scarce compensate the neglect of the smallest active duty.” source