Self-generated thought has an important impact on attitude change, with repeated demonstrations of increased opportunity for thought about an attitude object increasing attitude extremity. The traditional explanation for this mere thought effect is that more time to think allows people to produce more attitudeconsistent thoughts, which polarize their attitudes. Expanding on this structural perspective, the current research explores a metacognitive account for the effect of time on attitude polarization. Three experiments demonstrate that thought confidence plays an independent mediating role in the mere thought effect (Experiment 1), that it accounts for reversals in the mere thought effect when people have too much time to think (Experiment 2), and that this reversal is tied to the difficulty people have retrieving thoughts when too much time is provided (Experiment 3). Thus, taking metacognitive features of thought into account sheds new light on self-persuasion in the mere thought paradigm.