It is impossible to examine every item in this universe, just as it is impossible to examine every child in the universe.
Research involves sampling the reality inside the box to learn about it.
If we see a pattern in the samples drawn from the box, then we can begin to predict the contents of the box. The goal of scientific activity is to accurately predict what we'll draw from the box. Let's say the first item a researcher draws randomly from the box is a drinking glass. It is impossible to predict the nature of the other items in the box from one item-a case study. A case study out of the context of other research is not very informative.