How Truth Governs Belief

Why, when asking oneself whether to believe that p, must one immediately recognize that this question is settled by, and only by, answering the question whether p is true? Truth is not an optional end for first-personal doxastic deliberation, providing an instrumental or extrinsic reason that an agent may take or leave at will. Otherwise there would be an inferential step between discovering the truth with respect to p and determining whether to believe that p, involving a bridge premise that it is good to believe the truth with respect to p. But there is no such gap between the two questions within the first-personal deliberative perspective; the question whether to believe that p seems to collapse into the question whether p is true.