Data documenting poor understanding among research participants and real-time efforts to assess comprehension in large-scale studies are focusing new attention on informed consent comprehension. Within the context of biobanking consent, we previously convened a multidisciplinary panel to reach consensus about what information must be understood for a prospective participant's consent to be considered valid. Subsequently, we presented them with data from another study showing that many U.S. adults would fail to comprehend the information the panel had deemed essential. When asked to evaluate the importance of the information again, panelists' opinions shifted dramatically in the direction of requiring that less information be understood. Follow-up interviews indicated significant uncertainty about defining a threshold of understanding and what should happen when prospective participants are unable to grasp key information. These findings have important implications for urgently needed discussion of whether consent comprehension is an ethical requirement or an ethical aspiration.