What does the efficient market hypothesis mean for investing?

The efficient market hypothesis is the theory that asset prices reflect all available information, making it hard to beat the market return consistently while taking the same risk.

It is divided into weak, semi-strong and strong forms according to how much information is reflected, and the semi-strong form, which holds that public information is immediately reflected in prices, is considered the most realistic. Behavioral economists, on the other hand, argue that markets are not fully efficient because of cognitive biases such as overconfidence.