Difference between objective and subjective distributions in asset pricing models? How does one differentiate between "objective" and "subjective" probability distributions in asset pricing models?

In asset pricing, economists often make a distinction between the "subjective" and the "objective" probabilities of future states of the world. What do they mean by this?
Probability judgments are based on an investors' private information sets, i.e. subjective probabilities. In contrast, objective probabilities are the underlying real probabilities that the world will end up in some state. It is necessary to make the distinction because traders do not have perfect information. See Markowitz (1991) for further explanation.

But objective probabilities remain a remarkable concept. If the market reveals objective probabilities, then these are in fact known, and traders can update their subjective probabilities accordingly. But if all traders agree on the probability distributions, they would have very little reason to trade. Hence one implication of portfolio theory is that there is too much trading going on. See Odean (1999) for empirical work on this, or Grossman &amp; Stiglitz (1980) for a theoretical critique.