The Buddhist tradition names four boundless states of mind, the good habits a person can cultivate until they become as wide as the sky. Three of them are easy to admire from a distance: loving-kindness toward all, compassion for those who suffer, and the steady evenness that neither clutches nor flinches. The fourth is the strange one. It is called mudita, sympathetic joy, and it asks for something oddly difficult — to be glad, actually glad, when good fortune lands on someone else. Not tolerance of their luck, not a polite nod at their promotion or their windfall or their happy marriage, but a genuine lift of the heart, as if the good thing had happened nearby and that were enough.
Teachers of the tradition tend to call this the hardest of the four, and the reason is honest. Compassion meets another person at their lowest, where no rivalry lives; it costs little to feel for someone who has less. Sympathetic joy arrives at exactly the moment envy is most tempting, when another has what one wanted, and it insists on rejoicing anyway. The Dhammapada keeps returning to the picture of a mind that has learned to feed itself this way rather than on grievance. In its verses on the happy life it offers a startling image of people who own almost nothing and lack for nothing:
Let us live most happily, possessing nothing; let us feed on joy, like the radiant gods.
To feed on joy is the point. Envy treats another's happiness as a subtraction from one's own store, as though there were a fixed quantity of good in the world and every share handed elsewhere left less on the table. Sympathetic joy treats it as addition. The store grows each time attention widens to include someone else's good luck as a thing worth celebrating rather than auditing.
Seneca arrives at nearly the same economy from the opposite door. In his long treatise on giving and receiving well, he studies what happens between people when a kindness passes from one hand to another, and he insists that the gift is only half the transaction. The other half is how it is received. The person who takes a good turn with real gladness, he writes, has already paid back the first installment of the debt — the receiving, done warmly, is itself a kind of giving. Gratitude, in his telling, is never a passive posture. It multiplies the good it touches, sending some of the warmth back to its source.
Put the two together and a small discipline appears. The person who has learned to be glad at another's table is not being generous with something scarce. Joy, it turns out, is one of the few goods that grows when it is shared and shrinks when it is hoarded — so the widest life may simply belong to whoever is willing to celebrate the most.