"She doesn't understand the concept of Roman numerals. She thought we just fought in world war eleven"

This quote by Joan Rivers is a funny jab at someone's absence of knowledge about Roman characters. It suggests that the person in concern is not extremely experienced about history or mathematics. The joke is that the individual thinks that World War II was the eleventh war, when in reality it was the 2nd. This is an amusing method of pointing out the person's lack of understanding in an easy going way. It is also a suggestion that it is very important to stay informed and educated about the world around us. The quote is a funny way of mentioning the significance of education and knowledge.