Even as stock markets sank again, one person (or group) made a lot of money this past week: the yet-to-be-identified holder of the single ticket that won the Mega Millions lottery. The lucky winner or winners hit a jackpot worth $1.54 billion in estimated annuity value (or $878 million in cash).

Only days ago, the scramble to buy tickets was highlighting some basic aspects of human nature: Money isn’t only about wealth, and people don’t understand probability. What’s more, the feeling of control can lead any of us to take...