Grossman-Stiglitz paradox

From Wilmott Wiki

The Grossman-Stiglitz paradox says that if a market were informationally efficient, that is, all relevant information is already reflected in market prices, then no single agent would have sufficient incentive to acquire the information on which prices are based.

This is of importance also in derivatives where it means that there is no incentive to forecast volatility if future volatility is already contained in the market prices of options.