Someone creates a class or series of classes for something, the classes are big in size with large complicated methods. The effort is a sea of technical debt for the entire team but in the thick of the daily chaos it is lost. With out the coder talking to the team, with no team code policy and no code reviews (and action points) it remains. Pretty soon the team forget about that code.

A few weeks\months\years goes by, some of the team may have left, some may remain but business asks for the team to add to that code. The team is now looking at a black hole, no one knows how it works, what it does, what it is for, it is a smelly hell hole and the deadline is fast approaching.

The team now tries to change the code, with no approach at unit tests or refactoring in fear of breaking the black hole the team do just that and the business have just lost money.

If you are faced with a black hole you need to look back over my series, even a black hole in what might seem like a clean unit tested application. Don't be fooled into thinking that legacy code does not apply to your code base. 

The next stage is don't let blackholes in your codebase. Effective code reviews, team communication and good overal team coding policies will really help. Even if you are faced with a deadline do not let them appear, stop, take stock, what can be done and who can help. If you allow them through they will grow and grow and grow and the technical debt will hit you like a tidal wave soon enough,.