This dissertation examines how we ought to reason about propositions whose truth is determined by whether we believe them. In it, I defend the thesis that in cases of self-fulfilling belief we ought to believe whatever would be best, if true. Though believing whatever would be best if true appears to be a form of wishful thinking, and so unwarranted, this dissertation develops an account according to which, when a belief is self-fulfilling, optimistic reasons which show what we believe to be good can also be genuine epistemic reasons for believing it to be true.