The Efficient Market Hypothesis (EMH) suggests that it's impossible to consistently beat the stock market because all available information is already reflected in stock prices. This means that investors can't buy undervalued stocks or sell overpriced ones. The EMH argues that the market is efficient and rational, making it hard to outperform the overall market through expert stock picking or timing. In an efficient market, new information is quickly incorporated into prices, making them the best estimate of an investment's value. This theory has been debated, especially in the context of the Indian stock market, where its limitations have been highlighted.