It all began with a stop at a red light.

Kevin Salwen, a writer and entrepreneur in Atlanta, was driving his 14-year-old daughter, Hannah, back from a sleepover in 2006. While waiting at a traffic light, they saw a black Mercedes coupe on one side and a homeless man begging for food on the other.

“Dad, if that man had a less nice car, that man there could have a meal,” Hannah protested. The light changed and they drove on, but Hannah was too young to be reasonable. She pestered her parents about inequity, insisting that she wanted to do something.

“What do you want to do?” her mom responded. “Sell our house?”

Warning! Never suggest a grand gesture to an idealistic teenager. Hannah seized upon the idea of selling the luxurious family home and donating half the proceeds to charity, while using the other half to buy a more modest replacement home.

Eventually, that’s what the family did. The project  crazy, impetuous and utterly inspiring  is chronicled in a book by father and daughter scheduled to be published next month: “The Power of Half.” It’s a book that, frankly, I’d be nervous about leaving around where my own teenage kids might find it. An impressionable child reads this, and the next thing you know your whole family is out on the street.