Money
Everyone says money doesn’t buy happiness, but it clearly has something to do with it. You can’t be very happy if you’re deeply in debt and about to lose your house because you don’t have enough money to make the mortgage payments, for instance. So some money is necessary, but it does have diminishing returns. Once you have all your basic needs met, and have enough to make yourself comfortable and do the things you enjoy, getting more money doesn’t really help an awful lot.