Being aware of someone else's existing knowledge is a prerequisite to effectively adapting an explanation to that person's learning needs. However, such knowledge awareness introduces the potential for motivated self-evaluation based on relative knowledge, that is, for social comparison. Because favorable social comparisons are actively defended, we propose that knowledge awareness might undermine information sharing in explanation when social comparison motives are active. We tested this hypothesis in a series of experiments in which participants provided explanations to an ostensible learning partner with or without knowledge awareness. Both dispositionally and situationally motivated social comparison interacted with knowledge awareness to reduce information sharing in explanation. Intriguingly, knowledge awareness uniformly facilitated adaptation of the information that was shared to address partner knowledge deficit. These results illustrate a tension in the components of effective explanation. At the same time that knowledge awareness effectively coordinates explanation content, it can lead to knowledge hoarding by knowledgeable explainers who are motivated to rely on knowledge differences between the self and the explanation recipient for self-evaluation.