The efficient market hypothesis assumes that investors would always act rationally on the market and state that no investor would be able to earn abnormal returns consistently.Many investors, especially individuals who are subject to cognitive biases, are still acting irrationally on the market. Critically explain how those irrational behaviour would affect the validity of the efficient market hypothesis.

Evidence shows that there are investors on very efficient markets are still earning very good returns over the long term. Critically comment on how the market could still be efficient and allow those investors to earn abnormal returns.