Much research on explanation has focused on the ability of explanations to draw upon relevant knowledge to aid in understanding some event or observation. However, explanations may also structure our understanding of events and related tasks more generally, even when they add no relevant information. In three experiments, we show that explanations affect performance in simple, binary decision tasks where they could not possibly add relevant information. Whereas people with no explanation for differences in event probabilities tended to probability-match, people with an explanation tended to over-match (behave more normatively). The results suggest that explanations play a role in structuring our understanding of events, in addition to adding relevant information.