"You need to understand beautiful code to get to understand beautiful-enough code."
~ Dan North
Small drops and quotes about software craftsmanship
"The important point is that the cost of adding a feature isn't just the time it takes to code it. The cost also includes the addition of an obstacle to future expansion. Sure, any given feature list can be implemented, given enough coding time. But in addition to coming out late, you will usually wind up with a codebase that is so fragile that new ideas that should be dead-simple wind up taking longer and longer to work into the tangled existing web. The trick is to pick the features that don't fight each other."
To paraphrase my mother, it's all fun and games until someone starts writing subclasses.
When the hierarchy is correct, anyone can successfully create a new subclass.