When you are a developer chances are somewhere along the line you encountered scope creep.
What is it?
Scope creep is when you work on a program for a client and the client keeps requesting additions or changes that go out of the scope of the original plan for the program.
This is a problem because when the development of a program starts the requirements are already specified and the quote / price for the development has been accepted and was based on the requirements of the program. When a client requests additional functionality that is not included in the price, it requires more hours of development, thus you or the company loses money on the project as more hours were spent on development than were originally quoted for.
This is not only a problem when it comes to programming but also any type of digital service like graphic design for instance.