We consider the role that memory and knowledge play in the accuracy of people's generation of top-10 lists. We report data from an experiment in which people answered questions like ``list the top 10 most watched TV shows in the US'', with and without the help of a memory aid that provided the true top 50 items. Our analyses examine the changes in accuracy resulting from the availability of the memory aid, the patterns with which people modify their lists when the aid is provided, and the stability of individual differences in the memory and decision-making processes involved. We find clear evidence that, for those involving large number of potentially relevant items, memory retrieval plays a central role in determining the accuracy of the list. We discuss implications of these findings for the development of models for aggregating rank orders produced by people when not given the relevant items.