Centuries ago, English communities would walk the little boys around the perimeter of their parish as a way of preserving land records. This was called “beating the bounds.” The idea was that by teaching the boundaries to someone young, the knowledge would be preserved for the lifespan of that person. Of course modern geological survey techniques make beating the bounds unnecessary.
Software development hasn’t reached the sophistication of geographic survey. Many software shops use a knowledge management system remarkably similar to beating the bounds. They hire a new developer to work on a new project. That developer will remain tied to that project for the rest of his or her career, like a serf tied to the land. The knowledge essential to maintaining that project resides only in the brain of its developer. There are no useful written records or reliable maps, just like medieval property boundaries.
Update: Here’s a response from Johanna Rothman about how to avoid medieval project management.