Highly credible communicators have been found to elicit greater confidence and attitudes that are based more on recipients’ thoughts (i.e., self-validation) compared with non-credible sources. However, source credibility may produce different effects on thought confidence and persuasion depending on the position of an advocacy. When messages are proattitudinal, credible sources should initiate self-validation because recipients may be motivated to confirm (bolster) their existing views. Conversely, when appeals are counterattitudinal, recipients may be motivated to defend their opinions and disconfirm information. In these contexts, greater self-validation may emerge when a communicator lacks rather than possesses credibility. When a message was counterattitudinal and contained weak arguments, evidence of self-validation was found with low source credibility (Studies 1 and 2) and among participants high in defense motivation (Study 2). In response to strong, proattitudinal arguments, findings were consistent with high credibility producing self-validation when bolstering motivation was high (Study 3).