Ah, how little you know of human happiness - you comfortable and benevolent people! For happiness and unhappiness are brother and sister - or even twins who grow up together - or in your case - remain small together!
In our concern for others, we worry less about ourselves. When we worry less about ourselves an experience of our own suffering is less intense. What does this tell us? Firstly, because our every action has a universal dimension, a potential impact on others' happiness, ethics are necessary as a means to ensure that we do not harm others. Secondly, it tells us that genuine happiness consists in those spiritual qualities of love, compassion, patience, tolerance and forgiveness and so on. For it is these which provide both for our happiness and others' happiness.
To be satisfied with a little, is the greatest wisdom; and he that increaseth his riches, increaseth his cares; but a contented mind is a hidden treasure, and trouble findeth it not.
Hume's doctrine was that the circumstances vary, the amount of happiness does not; that the beggar cracking fleas in the sunshine under a hedge, and the duke rolling by in his chariot, the girl equipped for her first ball, and the orator returning triumphant from the debate, had different means, but the same quantity of pleasant excitement.