It all began with a stop at a red light. Kevin Salwen, a writer ... 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. [Hannah] 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: The Power of Half. Mr. Salwen and his wife, Joan, had always assumed that their kids would be better off in a bigger house. But after they downsized, there was much less space to retreat to, so the family members spent more time around each other. A smaller house unexpectedly turned out to be a more family-friendly house."We essentially traded stuff for togetherness and connectedness," Mr. Salwen [said], adding, "I can't figure out why everybody wouldn't want that deal."