The Efficient Market Hypothesis evolved in the 1960s from the Ph.D. dissertation of Eugene Fama. Fama persuasively made the argument that in an active market that includes many well-informed and intelligent investors, securities will be appropriately priced and reflect all available information. If a market is efficient, no information or analysis can be expected to result in outperformance of an appropriate benchmark.
Faced with the inference that they cannot add value, many active managers argue that the markets are not efficient (otherwise their jobs can be viewed as nothing more than speculation). Similarly, the investment media is generally considered to be ambivalent toward the efficient market hypothesis because they make money supplying information to investors who believe that the information has value (beyond the time when it initially becomes public). If the information is rapidly reflected in prices, there is no reason for investors to seek (or purchase) information about securities and markets.
Although this is a much discussed subject, no discussion of financial markets can avoid this issue.