A poorly planned implementation generally results in an incredibly patch-worked system. Many times when someone decides to jump the gun and get things started before the full realization of a realistic plan, it falls under 1 of 2 categories.
1) Experimentation - The client is not fully sure yet of what the end goal will be, so they add this and remove that and try the other until they work out the system as they want it to be. After a full realization of the intended system and it's workings, the system is rebuilt from the ground up.