“For a rational actor, the information he uses to shape his beliefs is a variable rather than a given. Before deciding how to act, he has to make a preliminary decision concerning the quantity of resources he is prepared to invest in looking for the relevant facts. A general must not attack before he has surveyed the terrain, or a surgeon operate before he has examined the patient. However, they must not delay too long, for then they may be surprised by the enemy’s attack or flight, or by the patient’s death.”