In the Zhuangzi (say "jwahng-dzuh"), a keeper of monkeys, handing out their acorns, tells them: "In the morning I will give you three (measures) and in the evening four." They're all angry, so he says: "Very well. In the morning I will give you four and in the evening three." Now they're pleased. The book calls the two offers "substantially the same," and it's seven acorns either way, though that's our arithmetic and not the text's. Notice that the keeper doesn't explain to the monkeys that the totals match. He just swaps them. A good share of what gets fought over at home has the same total in a different order, like who drives there and who drives back, or dishes now versus dishes after the show. If one of those comes up today, add up both versions before you argue, and when they come to the same seven, hand over the four in the morning.