Why is it so important that we protect these sources and that we enable journalists to do so? Well, I think there's one pretty critical reason, and that's that if you don't do it—and it is the responsibility of the journalist—you're very unlikely to gain the trust of anyone ever again. Nobody is going to talk to you any more. But, more seriously, those sources may have really serious cause to fear reprisals, either physical, economic, or professional. 