Network security vs. app security: What's the difference, and why does it matter?

If you’re familiar with the film The NeverEnding Story, then you know that the goal of the hero, Atreyu, was to reach the boundaries of Fantasia. He’s disappointed to learn that Fantasia has no boundaries because it’s the land of human fantasy. 
In some ways, the land of Fantasia is like network security. Where once there existed a fortress around the perimeter of a land that needed to be protected, those boundaries have expanded, leaving security professionals scratching