Efficient-market hypothesis
ECONOMIC THEORY THAT ASSET PRICES FULLY REFLECT ALL AVAILABLE INFORMATION, SO THAT IT IS IMPOSSIBLE TO "BEAT THE MARKET" CONSISTENTLY ON A RISK-ADJUSTED BASIS
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The efficient-market hypothesis (EMH) is a hypothesis in financial economics that states that asset prices reflect all available information. A direct implication is that it is impossible to "beat the market" consistently on a risk-adjusted basis since market prices should only react to new information.