There's some story (that I can't find online now) about a group going on a 24 hour journey through a desert. Just before they enter the desert, a man says to them that in the midst of night, they are about to cross a river. "Take as many rocks from the river bed as you can. The next day, you all will be equally sad and happy at the same time." The group indeed crosses a river in the night, and each of the party take a couple of rocks. Some just what they can carry themselves, some what their horse can hold. The next day, when they leave the desert, they discover that the rocks were precious stones (or rocks with gold encased). And everyone in the group is comparably joyful about their new wealth, and comparably sad that they didn't take more rocks.