The Cake-Cutting Rule

Two children fought over cake. Every time the mother cut it, one child complained the other got more.

So the mother made a new rule: one child cuts, the other chooses.

The cutter now had every incentive to divide precisely, because the chooser would take the larger piece. No threats were needed. No monitoring. The rule itself aligned selfishness with fairness.

The mother didn’t change the children. She changed the rules. The outcome she wanted — fair division — emerged naturally from the incentives she designed.