A financial market is an "efficient market" if its prices take into accounts all knowledge which people have about that market. (Notice that the use of the word "efficiency" in this context is not the same as the the use of the word in most of microeconomics.) If there is knowledge which is not being used, unexploited profit opportunities exist, and in financial markets these opportunities should be quickly taken. If one knows that a stock or bond is undervalued and that it will rise in value, one will make a large amount of money by buying until it does rise. Because profit opportunities are quickly exploited once they become known, one cannot "beat" an efficient market unless one has special information that is unavailable to others.