This article addresses the question whether we can know on the basis of folk intuitions that we have character traits. I answer in the negative, arguing that on any of the primary theories of knowledge, our intuitions about traits do not amount to knowledge. For instance, because we would attribute traits to one another regardless of whether we actually possessed such metaphysically robust dispositions, Nozickian sensitivity theory disqualifies our intuitions about traits from being knowledge. Yet we do think we know that we have traits, so I am advancing an error theory, which means that I owe an account of why we fall into error. Why do we feel so comfortable navigating the language of traits if we lack knowledge of them? To answer this question, I refer to a slew of heuristics and biases. Some, like the fundamental attribution error, the false consensus effect, and the power of construal, pertain directly to trait attributions. Others are more general cognitive heuristics and biases whose relevance to trait attributions requires explanation and can be classed under the headings of input heuristics and biases and processing heuristics and biases. Input heuristics and biases include selection bias, availability bias, availability cascade, and anchoring. Processing heuristics and biases include disregard of base rates, disregard of regression to the mean, and confirmation bias.