“ So true it is that the minds of men are easily shaken and carried off from their own sentiments through the casual commendation or reproof of others, unless the judgments that we make, and the purposes we conceive, be confirmed by reason and philosophy, and thus obtain strength and steadiness. ”
 Plutarch, Parallel Lives (c. 100 AD). copy citation

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“But through the care and diligence of his friends, who were very instant with him, and added force to their entreaties, he came to resolve and promise at last, that he would endure living, provided it might be in solitude, and remote from company; so that, quitting all civil transactions and commerce with the world, for a long while after his first retirement he never came into Corinth, but wandered up and down the fields, full of anxious and tormenting thoughts, and spent his time in desert places, at the farthest distance from society and human intercourse. So true it is that the minds of men are easily shaken and carried off from their own sentiments through the casual commendation or reproof of others, unless the judgments that we make, and the purposes we conceive, be confirmed by reason and philosophy, and thus obtain strength and steadiness. An action must not only be just and laudable in its own nature, but it must proceed likewise from solid motives and a lasting principle, that so we may fully and constantly approve the thing, and be perfectly satisfied in what we do; for otherwise, after having put our resolution into practice, we shall out of pure weakness come to be troubled at the performance, when the grace and goodliness, which rendered it before so amiable and pleasing to us, begin to decay and wear out of our fancy; like greedy people, who, seizing on the more delicious morsels of any dish with a keen appetite, are presently disgusted when they grow full, and find themselves oppressed and uneasy now by what they before so greedily desired.” source