Lets imagine you have a long code, and in the beginning you specified a library and a namespace, for example std
"using namespace std;" because you simply dont want to keep writing std::cout all the time. The problem that you may encounter is called a namespace clash, were a library might have several different namespaces for the same word. Put in another way, there might other stuff that cout means. And as said, if you have a long code you might end up being confused wether its std::cout or some other namespace.
