"Each person, then, is subject to two quite different requirements in connection with any proposition he considers: (1) he should try his best to bring it about that if that proposition is true then he believe it; and (2) he should try his best to bring it about that if that proposition is false then he not believe it. Each requirement by itself would be quite simple: to fulfill the first, our purely intellectual being could simply believe every proposition that comes along; to fulfill the second, he could refrain from believing any proposition that comes along. To fulfill both is more difficult. If he had only the second requirement—that of trying his best to bring it about that if a proposition is false then he not believe that proposition—then he could always play it safe and never act at all, doxastically. But sometimes more than just playing it safe is necessary if he is also to fulfill the first requirement: that of trying his best, with respect to the propositions he considers, to believe the ones that are true."