We know that we can learn much from the reports of multiple competent, independent, unbiased observers. There are also things we can learn from the reports of competent but biased observers. Specifically, when reports go against the grain of an agent's known biases, we can be relatively confident in the veracity of those reports. Triangulating on the truth via that mechanism requires a multiplicity of observers with distinct biases, each of whose reports might be one-way decisive in that fashion. It also presupposes that all observers share the same fundamental epistemic standards.