Translation: Efficient Market Hypothesis = Efficient Market Hypothesis (the belief that asset prices always reflect all available information).

Simplified Definition: The Efficient Market Hypothesis means that the current stock price reflects all known information, news, and expectations about it at this moment. In other words, markets are incredibly fast at absorbing any new information (whether positive or negative) and adjusting the price based on it immediately, making it almost impossible to "beat the market" or consistently achieve above-average returns simply by reading news or analyzing past data.

What does it mean for you?

  • Passive investing is easier: If the market is efficient and prices everything accurately, the best (and cheapest) strategy for you is to invest in exchange-traded index funds (which track the entire market) rather than trying to "hunt" for specific stocks.
  • Old news doesn't help: Don't expect to buy a stock and profit from it based on news you just read in the newspaper; millions of investors worldwide may have read it before you, and the market has already adjusted the price accordingly.
  • Surprises drive the market: Prices only jump or crash significantly if completely new and unexpected information appears that nobody anticipated.

Frequently Asked Question: If the market is "efficient" and perfect, how do some investors (like Warren Buffett) achieve returns that beat the market for many years?

Answer: This is the secret that makes this hypothesis just a "hypothesis" and not a strict law! Opponents see the market as not 100% efficient all the time; because investors are ultimately "human" and overreact due to fear or greed. Sophisticated investors exploit periods of panic (when prices fall below true value) or periods of excessive hype to achieve exceptional returns that the hypothesis cannot explain.