That's a very great question. Part of the understanding of little Johnny is that he's probably surrounded by people around him who are actually practising and working in those areas. Other people, such as friends, relatives, and neighbours, talk about it. They know about things. They come home and they hear the different things that are talked about. Little Julie doesn't have anybody around her in her surroundings who says “This is what I do”.
On March 31st, 2010. See this statement in context.