As was pointed out in Object-Oriented Analysis and Design with Applications (page 28), the role of a software development team is to engineer the illusion of simplicity.
As stated starting on page 12 here, and similarly here, by Grady Booch, there are five common characteristics to all complex systems:
The process of defining requirements usually results in incomplete specifications and incorrect specifications. A study in 1999 of requirements specifications found that they are typically only 7% complete and 15% correct.