Today, Joel Spolsky hits the sweet spot of what he does best - explain the mechanism of software development at a business level. It's a great column, and managers everywhere would be well advised to read it. The summary explains via an analogy - read the whole thing:

Nobody expects Dolly Parton to know how to plug in a microphone. There's an incredible infrastructure of managers, musicians, recording technicians, record companies, roadies, hairdressers, and publicists behind her who exist to create the abstraction that when she sings, that's all it takes for millions of people to hear her song. All the support staff and management that make Dolly Parton possible can do their jobs best by providing the most perfect abstraction: the most perfect illusion that Dolly sings for us. It is her song. When you're listening to her on your iPod, there's a huge infrastructure that makes that possible, but the very best thing that infrastructure can do is disappear completely. Provide a leakproof abstraction that Dolly Parton is singing, privately, to us.

That's how a productive business entity runs