Tranquility of our mind

The great source of both the misery and disorders of human life, seems to arise from over-rating the difference between one permanent situation and another... Some of those situations may, no doubt, deserve to be preferred to others; but none of them can deserve to be pursued with that passionate ardour which dirves us to violate the rules either of prudence or of justice; or to corrupt the future tranquility of our minds, either by shame from the remembrance of our own folly, or by remorse from the horror of our own injustice.

Taken from "The Theory of Moral Sentiments" by Adam Smith.