Drawn to my laptop in search of old Christmas songs and related nonsense, I spent a lot of time searching the obscure corners of YouTube during the holiday season. Of course, like our attics and our basements, once you start poking around You Tube, you’re bound to uncover a lot of things you weren’t looking for. My explorations took me somewhat circuitously from The Roches video rendition of The Hallelujah Chorus , to Leonard Cohen’s haunting masterpiece Halllelujah , to 2010’s Hope for Haiti Concert where Justin Timberlake covered that same song. Timberlake did a good job but, more than his performance, the concert itself has stuck with me ever since. I can’t stop thinking about its simplicity. A handful of singers each sang a song. Some celebrities answered a few phone calls. And millions of Americans texted, called or clicked in relatively small donations. Just like that, a charity that didn’t exist two weeks earlier raised more money in two hours than most non-profits will...