Overestimation of one’s ability to argue their position on socio-political issues may partially underlie the current climate of political extremism in the U.S. Yet very little is known about what factors influence overestimation in argumentation of socio-political issues. Across three experiments, emotional investment substantially increased participants’ overestimation. Potential confounding factors like topic complexity and familiarity were ruled out as alternative explanations. Belief-based cues were established as a mechanism underlying the relationship between emotional investment and overestimation in a measurement-of-mediation and manipulation-of-mediator (...) design. Representing a new bias blind spot, participants believed emotional investment helps them argue better than it helps others ; where in reality emotional investment harmed or had no effect on argument quality. These studies highlight misguided beliefs about emotional investment as a factor underlying metacognitive miscalibration in the context of socio-political issues. (shrink)