You don’t necessarily have to know anything about a company for its stock to go up. But the important point is that (1) the oil experts, on average, are in a better position than doctors to decide when to buy or to sell Schlumberger; and (2) the doctors, on average, know better than oil experts when to invest in a successful drug. The person with the edge is always in a position to outguess the person without an edge—who after all will be the last to learn of important changes in a given industry.
