Despite that fact that architects and developers know that tight coupling leads to increased complexity, we experience large object models growing out of control on an almost daily basis. In practice, this leads to performance problems and lack of transactional integrity. There are many reasons why this happens: the inherent complexity of the real world, which has few clear boundaries; insufficient programming language support for dynamic multi-object grouping; and weak design practices.
Source: Einar Landre in “97 Things Every Programmer Should Know – Extended”, Shirish Padalkar, http://leanpub.com/97-Things-Every-Programmer-Should-Know-Extended