The instability of citizens' opinions has long troubled political scientists, challenging the notion of meaningful public opinion necessary for democratic representation. We argue against the traditional view that equates opinion stability with citizen competence, and propose that instability is a natural consequence of citizens being uncertain about what they think on some issues. Using a novel survey instrument that allows respondents to express opinion ambiguity, we categorize responses into three ambiguity levels. Our findings from a three-wave panel spanning one year and a persuasion experiment reveal that ambiguous opinions are less stable over time and more susceptible to persuasion, as predicted by our model. We conduct a wide range of further analyses and robustness checks showing that ambiguous attitudes, while unstable, often have a meaningful structure that can be used to predict changes over time. These results challenge previous assumptions equating unstable attitudes with "nonattitudes" and incompetence. We argue that citizens’ competence should be evaluated based on their ability to reflect on and express their certainty across issues, rather than solely on opinion stability. Our approach encourages a more nuanced understanding of opinion quality and its role in democratic representation.