Davidson, Donald - Subjective, Intersubjective, Objective

When a speaker avers that he has a belief, hope, desire or intention, there is a presumption that he is not mistaken, a presumption that does not attach to his ascriptions of similar mental states to others. Why should there be this asymmetry between attributions of attitudes to our present selves and attributions of the same attitudes to other selves? What accounts for the authority accorded first person present tense claims of this sort, and denied second or third person claims?