Repetition of an assertion increases the degree of belief in that assertion. This reiteration effect is used to explain two puzzling findings in research on hindsight bias. First, the reiteration effect explains the asymmetry in hindsight bias for true and false assertions. This striking asymmetry has often been observed in experimental studies, but no rationale has yet been found. Second, the reiteration effect predicts a novel finding: Recalled confidence will increase in hindsight bias studies even if no feedback is given. The authors have checked both predictions against results reported in the literature; with some exceptions, the evidence supports them.The aim of this article is to relate two hitherto unrelated phenomena in human confidence. These two phenomena are that (a) confidence in the truth of an assertion increases after the assertion is repeated, independent of its truth or falsity (e.g., Bacon, 1979;, and (b) recollection of confidence is systematically distorted after feedback about the actual truth or falsity has been received (known as "hindsight bias," e.g., Hawkins & Hastie, 1990). The effects of repetition and feedback on confidence are part of a group of puzzling phenomena related to human confidence that includes overconfidence, the hard-easy effect, and conservatism. Some two decades of research have yielded a rich phenomenology of these effects but have failed to produce theoretical models to describe the underlying cognitive processes. A consequence of this is that these phenomena are listed in textbooks side by side with little or no theoretical integration.This article seeks to provide a model for how two of these phenomena--the effect of repetition (which we term the reiteration effect) and the effect of feedback on confidence (the hindsight bias)--are linked. This article consists of three sections: a brief introduction of the reiteration effect and the hindsight bias; an exposition of the proposed model, including two predictions; and a test of these predictions. Foules (1895Foules ( /1995, an "affirmation, however, has no real influence unless it be constantly repeated, and so far as possible in the same terms. It was Napoleon, I believe, who said that there is only one figure in rhetoric of serious importance, namely, repetition. The thing affirmed comes by repetition to fix itself in the mind in such a way that it is accepted in the end as a demonstrated truth" (pp. 146-147). This rhetorical princip l e -r e i t e r a t i n g assertions to make them more believable--has been known and exploited by innumerable real and fictitious communicators throughout history, for instance, by Quintilian (quoted in Lausberg, 1990, p. 311), Ronald Reagan (Hertsgaard, 1988, and Marcus Antonius in Shakespeare's Julius Caesar ( 3.2.73 -107 ).In the last 20 years the relationship between repetition and degree of belief has been independently rediscovered in psychological laboratories and put to experimental test. seem to have been the first to demonstrate that (a) repetition of an assertion incr...