There has been an explosion of formal work in commonsense reasoning in the past fifteen years, but almost no significant connection with work in building commonsense reasoning systems (cognitive or otherwise). We explore the reasons, and especially the ideal formal assumption of omniscience, reviewing and extending arguments that this is irreparably out of line with the needs of any real reasoning agent. On the other hand, this exploration reveals some desiderata that might still be given useful formal treatment, but with a somewhat altered set of aims from what has motivated most formal work. The discussion is motivated by several examples of commonsense reasoning, involving change of belief in addition to the more usual arguments concerning resource limitations. Key to the entire discussion is the notion that real reasoners do not usually have the luxury of isolated problems with well-defined beginnings and endings, but rather must deal with evolving and ongoing problems and situations. (Also cross-referenced as UMIACS-TR-94-62)