“Priced in” is the proven false idea that markets are rational. Warren Buffet couldn’t have become a billionaire if “priced in” was true. Because otherwise there would never be undervalued companies to purchase.
The efficient market hypothesis does not claim anything about “rational”.
I’ll amend my statement. If markets were actually efficient then Warren Buffet couldn’t have become a billionaire because everything would have already been “priced in”.
This paper concludes that Buffett did essentially do factor-investing.
I don’t really understand why the efficient market hypothesis (EMH) and factor investing don’t contradict each other but smarter people think they don’t (e.g. Fama who co-invented both). The general consensus seems to be that the weak form of EMH is correct but the semi-strong and the strong EMH probably not. However, while markets may not be perfectly efficient they can still be very close. This is why I believe that “priced in” often works in practice and is a useful concept.