RealWorldProblems are exemplified by the way the nasty little details of reality conspire to bite theoreticians on the ass when the theoretician actually tries to do something non-theoretical. Typical example from physics: 1) assume a massless rope and a frictionless pulley are used by a physicist to lift a big weight... Result from the RealWorld when the theoretician actually tries it with a rope that has mass and a pulley that has friction... dead theoretician.
In theory, theory and practice are the same. In practice, they differ...
ShaggyDogStory? about a physicist who goes out into the countryside to give lectures. He stands up in front of the farmers and begins, "Assume a spherical cow of uniform density..."
Tips: In the real world, EverythingIsRelative, and the granularity of new requirements is often smaller than your existing "chunks". For example, you will need to override 1/3 of a method.