The first is to have an adequate model of the cognitive state of other agents. The second is to form plans under the constraint of resource limitations: i.e., an agent does not always have an infinite amount of time to sit and think of plans while the world changes under him; he must act. These two problems are obviously interlinked since, to have a realistic model of the cognitive states of other agents, who are presumably similar to himself, an agent must reason about the resource limitations they are subject to in reasoning about the world. In this paper we address both problems with reference to AI planning system robots and one part of their cognitive state, namely beliefs. Our goal is to pursue what might be called robot psychology: to construct a plausible model of robot beliefs by examining robots' internal representations of the world.