In an organization based on achievement and rewarding of merit through promotions, an employee will rise to his or her own level of incompetence, and stay there.
The principle was actually first formalized in a book, known as The Peter Principle. I was going to add a corollary to it, but I see there are already a few corollaries out there. So, I'll add an addendum:
Diligent, responsible employees will collect more and more responsibilities until they are paralyzed and ineffective.
I feel like that addendum helps describe why I haven't posted anything in nearly two months.