Some past events incite more wonder about their causes than do others. For example, negative events require explanation more than positive events. We review social psychologists’ theoretical and empirical insights on what kinds of past events “beg explanation.” We draw on attribution theory that became popular among psychologists from the 1960s onward, on research on counterfactual reasoning, and on conversational and discursive critiques of attribution theory. We argue that factors predicting what is or is not perceived as requiring explanation are culturally and historically grounded, and that accordingly, what begs explanation varies between contexts and can change over time. Yet, drawing on the distinction between content and process, we argue that there are recognizable patterns across time and space. Specifically, we propose the relationship between events and background expectations as a rather stable predictor of what begs explanation—and as a level of analysis that can unite seemingly disparate approaches.