Joy is a pleasant emotion, and we gladly abandon ourselves to it upon the slightest occasion.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“who is put out of humour by the badness of the weather when in the country, by the badness of the roads when upon a journey, and by the want of company, and dulness of all public diversions when in town; such a person, I say, though he should have some reason, will seldom meet with much sympathy. Joy is a pleasant emotion, and we gladly abandon ourselves to it upon the slightest occasion. We readily, therefore, sympathize with it in others, whenever we are not prejudiced by envy. But grief is painful, and the mind, even when it is our own misfortune, naturally resists and recoils from it.” source