Worst Case Conditions

Hi I am studying Validation at the moment. I am doing an assignment and the question is discuss the concept of Worst case conditions in validation and give an example. Can some one help me with an example so that I can add to my assignment and understand the concept better. This is just a 2 page assignment so does not need to be complicated. I can understand the definition but can’t seem to be able to get my head round an example. Any help please…