In object-oriented languages there’s a nifty feature called code inheritance. People tend to think that this is a really cool ™ thing, since it allows you to quickly slab some new features onto a class whenever the need arises. In fact, there still seems to be a lot of folks who think that the whole point of object-orientation is to subclass a lot.
I’ve previously worked with Microsoft MFC, which was designed that way (but remember, that was back 1992) – as was the class hierarchy that makes your Unreal Tournament tick. I’ve seen object hierarchies spreading over 15 levels, and more.
The only problem with code written that way is that it sucks. A lot.